Focusing on the defect that existing literature does not explicitly model B2C sharing businesses as time-sharing rentals, this paper introduces the concept of efficiency of sharing service operations (ESSO), which captures the turnover rate of the shared product in serving consumers. The paper then develops and solves a two-stage game-theoretic model in which a manufacturer chooses its operational strategies from the following three strategies: Traditional sale, internal B2C sharing business extension, and external B2C sharing business extension, in stage 1. In stage 2, the manufacturer and a third-party B2C sharing platform (when the external B2C sharing business extension is chosen) make their specific operational decisions. By solving for the subgame perfect equilibrium, the following main results are obtained. 1) The necessary condition under which the manufacturer chooses the internal (external) B2C sharing business extension is that the ESSO of the manufacturer (the third-party B2C sharing platform) goes beyond a threshold, and given that this necessary condition is satisfied, the manufacturer chooses the external B2C sharing business extension if and only if the ESSO of the third-party B2C sharing platform is high enough (relative to the ESSO of the manufacturer) and the manufacturer’s ESSO is not too high. Otherwise, the manufacture will choose the internal B2C sharing business extension. 2) If the third-party B2C sharing platform is characterized by its ESSO and its ability to meet sharing demand, Result 1) still holds qualitatively for any given level of the ability to meet sharing demand. Additionally, a substitutive relationship exists between these two dimensions regarding their impacts on the manufacturer’s choice of the internal B2C sharing business extension. 3) From stakeholders’ perspectives, for a given level of the manufacturer’s ESSO, the optimal choice of its operational strategy results in a win-win-win scenario for the manufacturer, consumers, and the social planner if and only if the ESSO of the third-party B2C sharing platform is either high enough or low enough. Otherwise, it leads to some loss in either consumer surplus or social welfare.