Proofs
Proof of Proposition 1
I first prove the optimal pricing, discussed informally in Sect. 2. \(\square\)
Lemma 1
(Optimal Pricing) If the firm sells h to the whole market, then quality shoppers are indifferent between buying and not buying, and \(p^*_h = p_{Q,h}\). If the firm sells h to a fraction of the market, then conscious shoppers are indifferent between buying and not buying, and \(p_h^{**}= p_{C,h}\). If the firm sells m to the whole market, then all shoppers are indifferent, and \(p^*_m = p_{C,m}=p_{Q,m}\).
Proof of Lemma 1
Suppose to the contrary that Q are not indifferent when they buy product h at price \(p_h\); that is, \(V_Q(1;h) > V_Q(0;h)=0\). This implies \(p_h< p_{Q,h}= q(h, x_h) <q(h, x_h)+\theta \nu (h) = p_{C,h}\). Therefore, F could increase \(p_h\) by some amount \(\varepsilon\) without losing Q or C as customers, and F would strictly increase its profit. Hence, charging \(p_h < p_{Q,h}\) can never be optimal. At \(p^*_h= p_{Q,h}\), \(V_Q(1;h) = V_Q(0;h)=0\). The same logic applies in the other two cases.
The remainder of the proof proceeds in two steps: First, I derive the firm’s optimal effort and maximised profit for a given choice of production technology. Second, I compare the firm’s maximised profit across production technologies for different values of \(\theta\). Let \(q'(x_k) :=\frac{\partial q(x_k,k)}{\partial x_k}\).
First, suppose that \(k=m\). Given Assumption 2, I can focus on the case that F sells m to the whole market. From Lemma 1 and Assumption 1, F sets \(p_m^*= q(x_m,m) = A_m x_m\). Therefore, F’s profit from choosing the effort level is \(\Pi (p^*_m, x_m; m)= (C+Q)[q(x_m,m) - \frac{c_m}{2} x_m^2]=[A_m x_m - \frac{c_m}{2} x_m^2]\), which is maximised at \(x^*_m = \frac{q'(x_m^*)}{c_m}= \frac{A_m}{c_m}\). Consequently, F’s maximised profit is \(\Pi (p^*_m, x^*_m; m) = \frac{A_m^2}{2c_m}>0\). Therefore, given \(k=m\), the firm always chooses \((p^*_m,x^*_m)\) to sell to the whole market.
Now, fix \(k=h\). There are two scenarios: (i) selling to the whole market at \(p_h^*= q(x_h,h)= A_hx_h\); or (ii) selling to C only at \(p_h^{**}= q(x_h,h)+ \theta \nu (h)= A_hx_h + \theta\). Suppose \(p_h^*= A_h x_h\). Then F’s profit from choosing the effort level is \(\Pi (p^*_h, x_h; h)= (C +Q)[A_h x_h - \frac{c_h}{2} x_h^2]\) which is maximised at \(x^*_h = \frac{q'(x_h^*)}{c_h}= \frac{A_h}{c_h}\). Consequently, F’s maximised profit is \(\Pi (p^*_h, x^*_h; h) = \frac{A_h^2}{2c_h} >0\). Suppose \(p_h^{**}=A_h x_h + \theta\). Then, \(x_h^{**} = x_h^*\) with \(\Pi (p^{**}_h, x^{**}_h; h)= C\frac{A_h^2}{2c_h} + C\theta >0\). Therefore, given \(k=h\), the firm chooses to sell to C only at \(p_h^{**}\) over the whole market at \(p_h^*\) if
$$\begin{aligned} \Pi (p^{**}_h, x^{**}_h; h)= C\Pi (p^*_h, x^*_h; h) +C\theta &\ge \Pi (p^*_h, x^*_h; h), \nonumber \\ \theta&\ge \frac{1-C}{C} \Pi (p^*_h, x^*_h; h). \end{aligned}$$
(7)
Second, suppose (7) does not hold: F sells to the whole market under either production process. Then F prefers to produce product m over h if \(\Pi (p^*_m, x^*_m; m) > \Pi (p^*_h, x^*_h; h)\). Given \(c_h> c_m >0\), this rearranges to \(\big (\frac{A_m}{A_h}\big )^2 >\frac{c_m}{c_h}\). As \(\big (\frac{A_m}{A_h}\big )^2 \ge 1\) and \(1> \frac{c_m}{c_h}> 0\), the inequality always holds. If it is optimal to sell to the whole market, the profit is greater for \(k=m\). Now, suppose (7) holds: F sells h to a fraction of the market. Then F prefers to produce product h over m if
$$\begin{aligned} \Pi (p^{**}_h, x^{**}_h; h)= C\Pi (p^*_h, x^*_h; h) + C\theta &> \Pi (p^*_m, x^*_m; m), \nonumber \\ \theta&> \frac{1}{C} \Pi (p^*_m, x^*_m; m) - \Pi (p^*_h, x^*_h;h). \end{aligned}$$
(8)
Given that (8) is more stringent than (7), that is, \(\Pi (p^*_m, x^*_m; m) > \Pi (p^*_h, x^*_h; h)\), the equilibrium production technology is \(k=h\) whenever (8) holds. The condition rearranges to \(C\theta > Q \Pi (p^*_m, x^*_m; m) + C \big [\Pi (p^*_m, x^*_m; m)- \Pi (p^*_h, x^*_h;h)\big ]\), as is stated in the proposition. \(\square\)
Proof of Proposition 2
Define \(\bar{p}:=\bar{q}+\theta\) and \(\bar{x}:=\frac{\bar{q}}{h}\). First, note that the firm’s profit under a binding standard is \(\Pi (\bar{p}, \bar{x}; h)= C \Big [ \bar{q} + \theta - \frac{c_h}{2} \Big (\frac{\bar{q}}{A_h}\Big )^2 \Big ] < \Pi (p^{**}_h, x^{**}_h; h)\) when selling h to C. I am interested in the conditions under which the unregulated firm chooses to sell h to C, but the regulated firm chooses to sell m to the whole market:
$$\begin{aligned} \Pi (p^{**}_h, x^{**}_h; h)> \Pi (p_m^*,x_m^*;m) > \Pi (\bar{p}, \bar{x}; h). \end{aligned}$$
(9)
The second inequality in (9) rearranges as follows:
$$\begin{aligned} \Pi (p_m^*,x_m^*;m) = \frac{q(x_m^*,m)}{2} &> C \bigg [ \bar{q} + \theta - \frac{\bar{q}^2}{2q(x_h^{**},h)}\bigg ]= \Pi (\bar{p}, \bar{x}; h), \\ \quad \bar{q}^2 - 2 q(x_h^{**},h) \bar{q} + \frac{q(x_m^*,m)q(x_h^{**},h)}{C} - 2 q(x_h^{**},h) \theta &> 0. \end{aligned}$$
Given that \(\bar{q} > q(x_h^{**},h)\), the unique solution is
$$\begin{aligned} \bar{q} > q(x_h^{**},h) + \sqrt{q(x_h^{**},h)^2 - \frac{q(x_m^*,m) q(x_h^{**},h)}{C} + 2 q(x_h^{**},h) \theta } =:\check{q}. \end{aligned}$$
Note that the first inequality in (9) implies \(q(x_h^{**},h)> \frac{q(x_m^*,m)}{C}-2\theta\). Substituting for \(q(x_h^{**},h)\) yields
$$\begin{aligned} \check{q} > q(x_h^{**},h) + \sqrt{ q(x_h^{**},h) \Big (\frac{q(x_m^*,m)}{C}-2\theta \Big ) - \frac{q(x_m^*,m) q(x_h^{**},h)}{C} + 2 q(x_h^{**},h) \theta } = q(x_h^{**},h). \end{aligned}$$
\(\square\)
Proof of Proposition 3
First, in any such equilibrium the two firms must make the same profit. Otherwise, a firm would prefer to switch to the other production process, and try capturing the other firm’s shoppers. In particular, a firm can reduce the price or increase quality. However, I show that a quality increase is more costly. Hence, the firms compete in prices.
For example, an \(\varepsilon\) price reduction on h reduces profit by \(\Pi (p_h^{**}, x_h^{**};h) - \Pi (p_h^{**} - \varepsilon , x_h^{**};h) = C \varepsilon\), and increases C’s utility by \(\varepsilon\). An \(\varepsilon\) quality increase reduces profit by \(\Pi (p_h^{**}, x_h^{**};h) - \Pi (p_h^{**}, x_h^{**}+ \varepsilon ;h) = C A_h \varepsilon + C\frac{c_h}{2}\varepsilon ^2\), and increases C’s utility by \(A_h \varepsilon\). The profit reduction from a price discount is, thus, proportional to C’s utility increase. The profit reduction from a quality increase, in contrast, is more than proportional. In other words, a price discount is the more effective means: Profit is increasing linearly in price, whereas the effort to increase quality comes with a convex cost \(c(x_k)\).
Second, note that, if the other firm was not taken into account, \(F_i\) would set \(p_h^{**}\) and \(F_j\) would set \(p_m^*\) so as to extract all surplus from their respective shoppers. Given that \(\Pi (p_h^{**}, x_h^{**};h) \gtrless Q\Pi (p_m^*,x_m^*;m)\) and if I assume that price adjustment is one-sided, there are two ways to equate \(F_i\)’s and \(F_j\)’s profit: (i) \(F_i\) lowers \(p_h^{**}\) by \(\bar{\varepsilon }\) while \(F_j\) sets \(p_m^*\); or (ii) \(F_j\) lowers \(p_m^*\) by \(\hat{\varepsilon }\) while \(F_i\) sets \(p_h^{**}\). However, (ii) cannot be an equilibrium: C are indifferent between buying and not buying h at \(p_h^{**}\), but C are left with strictly positive utility from buying m at \(p_m^*- \hat{\varepsilon }= p_{C,m}- \hat{\varepsilon }\) with \(\hat{\varepsilon }\) implicitly defined by \(\Pi (p_h^{**}, x_h^{**};h) = Q \Pi (p_m^*-\hat{\varepsilon },x_m^*;m)\). Consequently, C would want to deviate to buying m.
In case (i), both C and Q are indifferent between buying and not buying m at \(p_m^*\), but C are left with strictly positive utility from buying h at \(p_h^{**} - \bar{\varepsilon }\). Therefore, I can focus on a deviation of Q. Quality shoppers do not have an incentive to deviate to buying h if \(\bar{\varepsilon }\) is sufficiently low:
$$\begin{aligned} V_Q(p_h^{**} - \bar{\varepsilon }, x_h^{**}) = V_Q(p_h^{**}, x_h^{**}) + \bar{\varepsilon } = A_h x_h^{**} - (A_h x_h^{**} + \theta ) + \bar{\varepsilon }&\le 0, \nonumber \\ \bar{\varepsilon }&\le \theta . \end{aligned}$$
(10)
The price discount that equates profits is given by
$$\begin{aligned} \Pi (p_h^{**} - \bar{\varepsilon }, x_h^{**};h) = C\Pi &(p^*_h, x^*_h; h) + C\theta - C\bar{\varepsilon } = Q \Pi (p_m^*,x_m^*;m), \nonumber \\ \bar{\varepsilon } &= \theta - \bigg [ \bigg (\frac{1-C}{C}\bigg ) \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h)\bigg ] . \end{aligned}$$
(11)
In the proposed equilibrium with a one-sided price reduction on h, \(F_i\) cannot have an incentive to deviate and reduce the price further to \(p_h^*\) such that Q switch to buying h:
$$\begin{aligned} \Pi (p_h^{**} - \bar{\varepsilon }, x_h^{**};h) = Q\Pi (p_m^*,x_m^*;m) &\ge \Pi (p_h^*,x_h^*;h), \nonumber \\ \frac{A_m}{A_h}&\ge \bigg [\frac{1}{1-C}\frac{c_m}{c_h}\bigg ]^{\frac{1}{2}}. \end{aligned}$$
(12)
Note that \(\frac{A_m}{A_h} \ge 1\) and \(\big (\frac{c_m}{c_h}\big )^{\frac{1}{2}} <1\). However, for \(C>0\), \(\big (\frac{1}{1-C}\big )^\frac{1}{2} > 1\). Therefore, (12) is not implied by the parameter restrictions but is necessary for equilibrium existence, which ensures that \(F_i\) does not have a profitable deviation. I will use (12) later to obtain the second condition in Proposition 3. Moreover, (12) implies that the second term on the right-hand side of (11) is strictly positive:
$$\begin{aligned} \bigg [ \bigg (\frac{1-C}{C}\bigg ) \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h) \bigg ] \ge \frac{1}{C} \Pi (p_h^*,x_h^*;h) - \Pi (p_h^*,x_h^*;h) = \frac{1-C}{C}\Pi (p_h^*,x_h^*;h)>0. \end{aligned}$$
Thus, substituting (12) into (11) implies that \(\bar{\varepsilon }< \theta\). Given that this condition is stronger than (10), Q do not have an incentive to deviate. Also \(F_j\) cannot have an incentive to deviate and reduce the price to such an extent that C switch to buying m. Under pricing strategy \(p_h^{**} - \bar{\varepsilon }\), C are left with strictly positive utility \(\bar{\varepsilon }\).
Therefore, \(F_j\) needs to reduce its price by \(\varepsilon \ge \bar{\varepsilon }\) to induce C to switch. To make such undercutting unprofitable for \(F_j\), \(\bar{\varepsilon }\) must be sufficiently large. In particular, setting \(p_m^* - \bar{\varepsilon }\) (or less) to sell to both Q and C must lead to a weakly lower profit for \(F_j\) than selling only to Q at \(p_m^*\):
$$\begin{aligned} Q \Pi (p_m^*,x_m^*;m)&\ge \Pi (p_m^*- \bar{\varepsilon },x_m^*;m) = \Pi (p_m^*,x_m^*;m) - \bar{\varepsilon }, \nonumber \\ \bar{\varepsilon }&\ge C \Pi (p_m^*,x_m^*;m). \end{aligned}$$
(13)
Substituting the price discount, given by (11), into (13) yields the first condition in the proposition:
$$\begin{aligned} \theta - \bigg [ \frac{1-C}{C} \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h) \bigg ] &\ge C \Pi (p_m^*,x_m^*;m), \nonumber \\ \quad \theta &\ge \bigg (C + \frac{1-C}{C}\bigg ) \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h). \end{aligned}$$
(14)
Note that this first condition implies also that the price discount is strictly positive. I can substitute further for \(\Pi (p_m^*,x_m^*;m)\) from (12) to obtain the second condition in the proposition:
$$\begin{aligned} \theta\ge \bigg (&C + \frac{1-C}{C}\bigg ) \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h) \\\ge & \bigg (C + \frac{1-C}{C}\bigg ) \bigg [\frac{1}{1-C} \Pi (p_h^*,x_h^*;h)\bigg ] - \Pi (p_h^*,x_h^*;h) = \bigg (\frac{C}{1-C} + \frac{1-C}{C}\bigg ) \Pi (p_h^*,x_h^*;h). \end{aligned}$$
Finally, note that the equal-profit constraint prevents \(F_i\) from selling h to C at a marginally higher price: \(F_i\) realises that this deviation results in zero profit. Suppose \(F_i\) plans to increase its price by \(\epsilon \in (0, \bar{\varepsilon })\). As C enjoy a strictly positive utility, they will continue to buy h. However, \(F_j\) expects \(F_i\) to make a higher profit: It would switch the production process, and would plan to offer h to C at a price \(p_h^{**} - \bar{\varepsilon } + \frac{\epsilon }{2}\). Price competition in h in this static setting implies that \(p_h = c(x_h^{**})\) instantaneously. Thus, \(F_i\) is better off selling at \(p_h^{**} - \bar{\varepsilon }\), and making profit \(\Pi (p_h^{**} - \bar{\varepsilon }, x_h^{**};h)>0\). \(\square\)
Proof of Proposition 4
First, the economic surplus when the two firms compete in selling m to the whole market is \(ESM :=(C+Q) A_m x_m^* - (C+Q)c(x_m^*) = \Pi (p_m^*, x_m^*;m)\). The specialised equilibrium is efficient if
$$\begin{aligned} ESS :=Q \Pi (p_m^*,x_m^*;m) + C\Pi (p_h^*, x_h^*;h) + C\theta &\ge \Pi (p_m^*, x_m^*;m) =:ESM, \nonumber \\ \theta&\ge \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*, x_h^*;h). \end{aligned}$$
(15)
Given that the specialised equilibrium exists, (14) holds and \(\big (C + \frac{1-C}{C}\big ) \Pi (p_m^*,x_m^*;m)> \Pi (p_m^*,x_m^*;m)\) for \(C \in (0,1)\). Therefore, the existence of a specialised equilibrium implies (15). \(\square\)
Proof of Proposition 5
First, \(F_i\) and \(F_j\) cannot have an incentive to merge to sell m to the whole market. Given that the firms share the monopolist’s profit equally, this implies
$$\begin{aligned} \Pi (p_h^{**} - \bar{\varepsilon }, x_h^{**};h) = Q \Pi (p_m^*,x_m^*;m) &\ge \frac{1}{2}(C+Q) \Pi (p_m^*,x_m^*;m), \\ \frac{1}{2}&\ge C. \end{aligned}$$
Second, \(F_i\) and \(F_j\) cannot have an incentive to merge to sell h to market segment C. This implies
$$\begin{aligned} \Pi (p_h^{**} - \bar{\varepsilon }, x_h^{**};h) = Q \Pi (p_m^*,x_m^*;m)&\ge \frac{1}{2}\Pi (p^{**}_h, x^{**}_h; h), \nonumber \\ Q \Pi (p_m^*,x_m^*;m)&\ge \frac{1}{2}[C\Pi (p^*_h, x^*_h; h) +C\theta ], \nonumber \\ \frac{2(1-C)}{C}\Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h)&\ge \theta . \end{aligned}$$
(16)
Proof of Corollary 1
From Proposition 3, given that a specialised equilibrium exists, (14) holds. Moreover, from Proposition 5, \(F_i\) and \(F_j\) do not have an incentive to collude as h-monopolist if (16) holds. Combining these inequalities yields
$$\begin{aligned} \frac{2(1-C)}{C}\Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h) \ge \theta \ge \bigg (C + \frac{1-C}{C}\bigg ) \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h). \end{aligned}$$
Therefore, if
$$\begin{aligned} \bigg (C + \frac{1-C}{C}\bigg ) \Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h)&> \frac{2(1-C)}{C}\Pi (p_m^*,x_m^*;m) - \Pi (p_h^*,x_h^*;h),\\ C + \frac{1-C}{C}&> \frac{2(1-C)}{C}, \end{aligned}$$
then merging to an h-monopolist in the specialised equilibrium is always profitable. Given that \(C \in (0,1)\), the above inequality is uniquely solved by \(C > \frac{\sqrt{5}-1}{2} =:\bar{C}\), where \(\bar{C} > \frac{1}{2}\). From the proof of Proposition 5, collusion as m-monopolist is profitable if \(C > \frac{1}{2}\). \(\square\)
Proof of Proposition 6
Because \(\varphi _H> \frac{1}{2} > \varphi _L\), conformist shoppers will convert into conscious shoppers if and only if the firm chooses handmade production. Therefore, the conjectured separating equilibrium exists if the firm prefers handmade production only after observing \(\varphi _H\), which is equivalent to \(\eta \in [\max \{0, \hat{\eta }(\varphi _H) \}, \hat{\eta }(\varphi _L)]\). Under Assumption 3,
$$\begin{aligned} \frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h) + \theta }&< 1, \\ [(1 - \varphi _L) - (1-\varphi _H)] \frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h) + \theta }&< (1-\varphi _L)\varphi _H - (1-\varphi _H)\varphi _L, \\ (1-\varphi _L)\frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h)} - (1-\varphi _L)\varphi _H&< (1- \varphi _H) \frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h)} - (1-\varphi _H)\varphi _L, \\ \hat{\eta }(\varphi _H) :=\frac{1}{1-\varphi _H}\bigg [ \frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h)} - \varphi _H\bigg ]&< \frac{1}{1-\varphi _L}\bigg [ \frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h)} - \varphi _L\bigg ] =:\hat{\eta }(\varphi _L), \end{aligned}$$
and
$$\begin{aligned} \frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h) + \theta }&< 1, \\ \hat{\eta }(\varphi _L) :=\frac{1}{1- \varphi _L}\bigg [\frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h) + \theta } - \varphi _L \bigg ]&< 1. \end{aligned}$$
Because \(\hat{\eta }(\varphi _H)< \hat{\eta }(\varphi _L) < 1\), the set is non-empty if \(0< \hat{\eta }(\varphi _L)\). This latter inequality rearranges to the condition \(\theta < \frac{\Pi (p_m^*, x_m^*;m)}{\varphi _L} - \Pi (p_h^*,x_h^*;h)\) in the proposition. If follows immediately that \(\theta < \Pi (p_m^*, x_m^*;m) / \varphi _H - \Pi (p_h^*,x_h^*;h)\) whenever \(0 < \hat{\eta }(\varphi _H)\).
Finally, I show that my assumption \(\eta \ge \tilde{\eta }(\varphi _H)\) is implied by \(\eta \ge \hat{\eta }(\varphi _H)\) so that the firm that sells a handmade product does not prefer deviating to \(p_h^*\) to sell also to quality shoppers:
$$\begin{aligned} \Pi (p_h^*, x_h^*;h)&< \Pi (p_m^*, x_m^*;m), \\ \tilde{\eta }(\varphi _H) :=\frac{1}{1- \varphi _H} \bigg [\frac{\Pi (p_h^*, x_h^*;h)}{\Pi (p_h^*,x_h^*;h) + \theta } - \varphi _H \bigg ]&< \frac{1}{1- \varphi _H} \bigg [\frac{\Pi (p_m^*, x_m^*;m)}{\Pi (p_h^*,x_h^*;h) + \theta } - \varphi _H\bigg ] =:\hat{\eta }(\varphi _H). \end{aligned}$$
\(\square\)