<p>Group buying platforms have emerged as well-structured marketplaces, attracting a significant number of consumers with attractive prices. While these platforms boost sellers’ sales through the group buying channel, they also create channel conflict by competing with the seller’s original channel. Consequently, sellers and group buying platforms must carefully deliberate on their cooperation modes: reselling or agency contract. Previous research has insufficiently explored how sellers and platforms select cooperation contracts in dual-channel settings. To address this gap, we construct a game-theoretical model to analyze the strategic interactions between sellers and platforms in a dual-channel structure under two different contracts. Our findings reveal several notable insights. First, under both contracts, prices in both channels decrease as peer influence efficiency increases. However, the impact of group buying effort costs on prices is nonuniform, diverging from prior findings. Second, both sellers and platforms benefit from peer influence, shedding light on the emphasis stakeholders place on leveraging peer influence in group buying strategies. Most importantly, we find that both parties are more inclined to adopt the agency contract only when the fixed commission rate is moderate. Finally, while competition between the group buying and direct channels intensifies under the agency contract, the overall performance of the supply chain improves.</p>