Appendix
Derivation of the equilibrium in the non-information sharing case
We find the sub-game perfect equilibrium by backward induction.
In Stage 4, given w, p and r, the retailer decides on whether to introduce the 3PP or not. When the 3PP does not exist, \( E\left[ {\hat{\pi }_{r} |\varepsilon = \hat{\varepsilon }} \right] = \left( {p - w} \right)\left( {1 - p + \hat{\varepsilon }} \right) \); when the 3PP exists, \( E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right] = \left( {p - w} \right)\left( {1 - Xp + \hat{\varepsilon }} \right) - rpq_{p} \). Hence, the retailer will introduce the 3PP if and only if \( E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right] \ge E\left[ {\hat{\pi }_{r} |\varepsilon = \hat{\varepsilon }} \right] \) i.e., \( r \le \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}} \); and the retailer will not introduce the 3PP if and only if \( E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right] < E\left[ {\hat{\pi }_{r} |\varepsilon = \hat{\varepsilon }} \right] \), i.e., \( r > \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}}. \)
In Stage 3, given \( w \) and \( p \), the 3PP decides on the commission rate \( r \) to maximize its profit given by:
$$ E[\pi_{p} |\varepsilon = \hat{\varepsilon }] = \left\{ {\begin{array}{*{20}l} {rp\left( {\lambda \left( {1 + \hat{\varepsilon }} \right) - (X + \lambda - 1} \right)p) - F} & {if} & {r \le \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}}} \\ 0 & {if} & {r > \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}}} \\ \end{array} } \right., $$
(9)
Setting \( r > \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}} \) leads to zero profit and is a dominated strategy for the 3PP. Thus, the 3PP’s optimal decision should satisfy \( r \le \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}} \), when we have \( \frac{{\partial E[\pi_{p} |\varepsilon = \hat{\varepsilon }]}}{\partial r} = pq_{p} \ge 0 \), i.e., the 3PP’s profit is non-decreasing in \( r \). The optimal decision of the 3PP is
$$ r^{N*} = \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}}. $$
(10)
In Stage 2, given \( w \), the retailer determines \( p \) to maximize its expected profit. Substituting Eq. (10) into \( E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right] \), we have:
$$ E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right] = \left( {p - w} \right)\left( {1 - Xp + \hat{\varepsilon }} \right) - \frac{{\left( {1 - X} \right)\left( {p - w} \right)}}{{\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p}}\left( {\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)p} \right)p. $$
(11)
Since \( \pi_{r} \) is concave in p\( \left( {\frac{{\partial^{2} E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right]}}{{\partial p^{2} }} = - 2 < 0} \right) \), we can obtain the best response p by solving the first order condition, \( \frac{{\partial E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right]}}{\partial p} = 0 \), i.e.,
$$ p = \frac{{w + 1 + \hat{\varepsilon }}}{2}. $$
(12)
In Stage 1, anticipating the best responses of the retailer and the platform, the manufacturer decides on the optimal \( w \) to maximize its expected profit given by:
$$ E\left[ {\pi_{m} } \right] = w\left( {1 - \frac{w + 1 + \xi }{2}X + \xi } \right), $$
(13)
subject to \( w < p \). Because \( E\left[ {\pi_{m} } \right] \) is a concave function in \( w \), we can derive the optimal decision by solving \( \frac{{\partial E\left[ { \pi_{m} } \right]}}{\partial w} = 0 \), i.e.,
$${w^{N*}} = \frac{{-\left({1+{\upxi}}\right){\text{X}}+2{\upxi}+2}}{2{\text{X}}}, $$
(14)
which self satisfies \( w < p \).
By substituting Eq. (14) into Eq. (12), we have the equilibrium retail price:
$$ p^{N*} = \frac{{\left( {1 - \xi + 2\hat{\varepsilon }} \right)X + 2\xi + 2}}{4X}. $$
(15)
By substituting Eqs. (14)–(15) into Eq. (10), we have:
$$ r^{N *} = \frac{{\left( {1 - X} \right)\left( {\left( {3 + 2\hat{\varepsilon } + \xi } \right)X - 2\xi - 2} \right)}}{{4X\lambda \left( {1 + \hat{\varepsilon }} \right) - \left( {\lambda + X - 1} \right)\left( {\left( {1 - \xi + 2\hat{\varepsilon }} \right)X + 2\xi + 2} \right)}}. $$
(16)
By substituting Eqs. (14), (15), and (16) into \( E\left[ {\pi_{m} } \right] \), \( E\left[ {\pi_{r} |\varepsilon = \hat{\varepsilon }} \right] \), and \( E[\pi_{p} |\varepsilon = \hat{\varepsilon }] \), we have:
$$ E[\pi_{m}^{N*} ] = \frac{{\left( {\left( {1 + \xi } \right)\left( {2 - X} \right)} \right)^{2} }}{8X}, $$
(17)
$$ E\left[ {\pi_{r}^{N *} |\varepsilon = \hat{\varepsilon }} \right] = \frac{{\left( {\left( {3 + \xi + 2\hat{\varepsilon }} \right)X - 2\xi - 2} \right)^{2} }}{{16X^{2} }}, $$
(18)
$$ E\left[ {\pi_{p}^{N*} |\varepsilon = \hat{\varepsilon }} \right] = \frac{{\left( {1 - X} \right)\left( {(3 + \xi + 2} \right)X - 2 - 2\xi )\left( {\left( {1 - \xi + 2\hat{\varepsilon }} \right)X + 2 + 2\xi } \right)}}{{16X^{2} }} - F. $$
(19)
The unconditional expected profits of the retailer and the 3PP are:
$$ E[\pi_{r}^{N *} ] = E\left[ E \right[\pi_{r}^{N *} |\varepsilon = \hat{\varepsilon }]] = \frac{{\xi^{2} }}{12} + \frac{{\left( {\left( {1 + \xi } \right)\left( {3X - 2} \right)} \right)^{2} }}{{16X^{2} }}, $$
(20)
$$ E[\pi_{p}^{N*} ] = E\left[ {E\left[ {\pi_{p}^{N*} |\varepsilon = \hat{\varepsilon }} \right]} \right] = \frac{{\left( {1 - X} \right)\left( {1 + \xi } \right)^{2} \left( {3X - 2} \right)\left( {2 + X} \right)}}{{16X^{2} }} - \frac{{\left( {1 - X} \right)\xi^{2} }}{6} - F. $$
(21)
Thus, the unconditional expected profit of the supply chain is:
$$ E[\pi_{c}^{N*} ] = \frac{{3\left( {1 + \xi } \right)^{2} \left( {4 - X^{2} } \right) - 4X\left( {12F - \left( {2X - 1} \right)\xi^{2} } \right)}}{48X}. $$
(22)
The equilibrium is summarized in Table 3.
Derivation of the equilibrium in the information sharing case
We derive the equilibrium by backward induction. In Stages 2–4, the decisions of the retailer and the 3PP are the same in the asymmetric and symmetric cases.
In Stage 1, anticipating the best responses of the retailer and the 3PP, the manufacturer decides on the optimal w to maximize its expected profit given by:
$$ E[\pi_{m} |\varepsilon = \hat{\varepsilon }] = w\left[ {1 - \frac{{\left( {w + 1 + \hat{\varepsilon }} \right)X}}{2} + \hat{\varepsilon }} \right], $$
(23)
subject to \( w < p \). Because \( E[\pi_{m} |\varepsilon = \hat{\varepsilon }] \) is a concave function of w, we can obtain the interior solution by solving \( \frac{{\partial E[\pi_{m} |\varepsilon = \hat{\varepsilon }]}}{\partial w} = 0 \), i.e.,
$$ w^{I*} = \frac{{\left( {1 + \hat{\varepsilon }} \right)\left( {2 - X} \right)}}{2X} , $$
(24)
which self satisfies \( w < p \).
By substituting Eq. (24) into Eq. (12), we have the equilibrium retail price:
$$ p^{I*} = \frac{{\left( {1 + \hat{\varepsilon }} \right)\left( {2 + X} \right)}}{4X}. $$
(25)
By substituting Eqs. (24)–(25) into Eq. (10), we have:
$$ r^{I*} = \frac{{\left( {1 - X} \right)\left( {3X - 2} \right)}}{{4X\lambda - \left( {\lambda + X - 1} \right)\left( {X + 2} \right)}}. $$
(26)
By substituting Eqs. (24), (25), and (26) into \( E[\pi_{p} |\varepsilon = \hat{\varepsilon }] \), \( E[\pi_{r} |\varepsilon = \hat{\varepsilon }] \), \( E[\pi_{m} |\varepsilon = \hat{\varepsilon }] \) we have:
$$ E[\pi_{p}^{I*} |\varepsilon = \hat{\varepsilon }] = \frac{{\left( {1 - X} \right)\left( {1 + \hat{\varepsilon }} \right)^{2} \left( {3X - 2} \right)\left( {X + 2} \right)}}{{16X^{2} }} - F, $$
(27)
$$ E[\pi_{r}^{I*} |\varepsilon = \hat{\varepsilon }] = \frac{{\left( {\left( {1 + \hat{\varepsilon }} \right)\left( {3X - 2} \right)} \right)^{2} }}{{16X^{2} }}, $$
(28)
$$ E[\pi_{m}^{I*} |\varepsilon = \hat{\varepsilon }] = \frac{{\left( {\left( {1 + \hat{\varepsilon }} \right)\left( {2 - X} \right)} \right)^{2} }}{8X}. $$
(29)
The unconditional expected profits of the 3PP, the retailer and the manufacturer are:
$$ E\left[ {\pi_{p} } \right]^{I *} = E\left[ {E\left[ {\pi_{p}^{I*} |\varepsilon = \hat{\varepsilon }} \right]} \right] = \frac{{\left( {\xi^{2} + 6\xi + 3} \right)\left( {1 - X} \right)\left( {3X - 2} \right)\left( {X + 2} \right)}}{{48X^{2} }} - F, $$
(30)
$$ E[\pi_{r} ]^{I *} = E\left[ E \right[\pi_{r}^{I*} |\varepsilon = \hat{\varepsilon }]] = \frac{{\left( {3X - 2} \right)^{2} (4\xi^{2} + 6\xi + 3)}}{{48{\text{X}}^{2} }}, $$
(31)
$$ E[\pi_{m} ]^{I *} = E\left[ E \right[\pi_{m}^{I*} |\varepsilon = \hat{\varepsilon }]] = \frac{{\left( {2 - {\text{X}}} \right)^{2} (4\xi^{2} + 6\xi + 3)}}{24X}. $$
(32)
Thus, the unconditional expected profit of the supply chain is:
$$ E[\pi_{c}^{I*} ] = \frac{{3\left( {1 + \xi } \right)^{2} \left( {4 - X^{2} } \right) + \left( {\left( {3X - 2} \right)^{2} + 2X\left( {X - 2} \right)^{2} } \right)\xi^{2} }}{48X} - \frac{{\left( {1 - X} \right)\left( {3X^{2} + 4X - 4} \right)\xi^{2} }}{{24X^{2} }} - F. $$
(33)
Overall, the equilibrium is concluded in Table 4.
Proof of Propositions 1–2
The results can be straightforwardly obtained by comparing the equilibrium with and without the 3PP, the details are omitted.
Proof of Propositions 3–4
The results can be straightforwardly obtained by comparing the equilibrium in the non-information sharing case and the information sharing case, the details are omitted.