To rank merchandise or a service based on the evaluation of a user, and to decide a price, and to provide the user initiated advertisements of merchandise or a service, and to execute price setting corresponding to evaluation or sales result.

This electronic commercial transaction service system for reflecting the evaluation and sales result of merchandise or a service purchased or used by a user on the price or evaluation of the merchandise is provided with a step for reflecting the evaluation of the merchandise or service purchased or used by the user, and for deciding the evaluation(rank) and price of the merchandise or service based on the evaluation or sales result. Thus, it is possible for the user to select the merchandise based on the objective evaluation of the merchandise or service from the user's point of view. Therefore, it is possible to execute price setting based on the sales result, and to use the high evaluation of the user as effective advertisements.