A method of selling a product online over the Internet is to be performed by a server device, and includes the steps of: a) configuring the server device to receive customer-identification information from at least one customer who has decided to purchase the product; b) configuring the server device to associate at least one of a plurality of identifiers with the customer-identification information; c) configuring the server device to select at least one of the identifiers according to a predetermined scheme when a predetermined termination condition is satisfied; and d) configuring the server device to conduct, with the at least one customer, transaction for the product. Whether or not a benefit associated with purchase of the product is provided to the at least one customer is based on the selected identifiers.