A store controller stores a series of prices for a product and respective effective periods during which the prices are effective. A customer submits an offer to buy the product at an "offer price" that is one of the series of prices. The offer also has an offer period that elapses when the respective effective period of the product price elapses. The offer period thereby defines a period during which the offer is effective and after which the offer cannot be accepted. Each offer further specifies (i) a customer identifier for identifying the customer, and (ii) funds or a payment identifier for specifying an account from which funds (typically the offer price) may be collected if the offer is accepted. The store controller then determines whether to accept the offer. If the offer is accepted, the store controller (i) initiates use of the payment identifier, if any, to collect the funds, and (ii) uses the customer identifier to identify the customer as having paid for the product. Thus, the customer pays for the product and the seller must deliver the product or otherwise inform the customer that the product has been sold to him.