Abstract: Based on the innovative marketing mode with two sale prices, over the last two years, online interpersonal group buying mode have rapidly become popular among many sellers and consumers in China. However, in relevant literature, there aren’t the theoretical analysis relating to the interpersonal group-buying mechanism or comparative studies of interpersonal group buying and traditional selling (such as uniform-pricing trading) have been found. In order to fill this research gap, the uniform-pricing trading for comparison is added in order to explore differences between interpersonal group buying and uniform-pricing trading in terms of profitability. In the research process, a theoretical model is provided to compare and analyze the impact of online interpersonal group-buying mode and the unified price mode (i.e., the normal mode) on the sellers, and reference for the sellers is provided to implement precision marketing. The consumers’ social relationship is considered and the consumers are subdivided, and then the cost coefficient of social relationship (i.e., social cost) and the impact of potential market demand on price and revenue are analyzed. The results show that, under certain conditions, the optimal price in the normal mode is between the optimal interpersonal group-buying price and the optimal normal price in the interpersonal group-buying mode. The optimal revenue in the normal mode is less than that in the interpersonal group-buying mode. That is, the interpersonal group buying mode can bring greater benefits to merchants, but the interpersonal group buying mode is only a supplement to the normal mode. Further, as the social cost difference between the two types of consumers gradually decreases or the potential market demand of consumers who prefer to interpersonal group-buying trading increases, the advantage of the interpersonal group-buying mode is gradually weakened. Therefore, it is suggested that the interpersonal group-buying platform cooperate with social platform (such as WeChat) to build a social e-commerce mode. The purpose is to reduce the social cost of consumers, so as to attract consumers to enter the interpersonal group-buying platforms to purchase goods, and achieve “sellers, platforms and consumers” multi-win. At last, it is suggested that the interpersonal group-buying platforms should subdivide the consumers in the second or third time and develop new market segments.

Key words: online interpersonal group-buying; social relationship (social cost); precision marketing; social e-commerce