Abstract: In recent years, the "one-out-of-two" arrangement proposed by B2C platforms to prevent the multi-ownership of merchants has been widely concerned by the industry. From the theoretical perspective, the "one-out-of-two" arrangement reflects the effect of exclusive trading contracts under the two-sided market structure. Taking the Hotelling Model as the basic framework and starting from the perspective of negotiation game between platforms and merchants, this paper introduces Nash bargaining model to explore the effect of B2C platform monopolistic transaction behavior. It is found that the bargaining power of merchants relative to the platform is an important factor to decide the exclusive transaction between merchants and platforms. When the bargaining power of merchants is in the middle or weak, the platform has a strong incentive to require merchants to sign an exclusive transaction agreement. From the perspective of competition effect, monopolistic trading contract will break the "competition bottleneck", restrain the market competition, and reduce the market share and profit level of the competitive platform. From the perspective of welfare effect, when consumer search cost is low, exclusive transaction does not always reduce consumer welfare and total social welfare with the increase of cross- network externality parameters and platform price subsidy. Based on the above analysis conclusion and the case of B2C platform exclusive trading, the corresponding anti-monopoly regulatory framework is proposed.

Key words: two-sided market, B2C platform, exclusive transaction, negotiation power, anti- monopoly