1. A method comprising: allowing a second merchant to intervene in a purchase by a customer of at least one item selected by the customer from a first merchant by providing an offer, associated with the purchase, for a subsidy from the second merchant, via a web site before the at least one item is purchased by the customer, the offer requiring the customer to agree to participate in an additional transaction with the second merchant; transmitting to the customer an indication of the at least one item; transmitting to the customer an indication of a cost to the customer for the at least one item; transmitting to the customer an indication of an associated first cost to the customer for the at least one item; receiving, by the merchant server, an indication that the customer accepts the offer associated with the purchase for the subsidy from the second merchant to be applied in association with a purchase of the at least one item from the first merchant, the offer requiring the customer to agree to participate in an additional transaction with the second merchant; in response to receiving the indication of the acceptance of the offer, reducing by the merchant server a cost of the at least one item for the customer from the first cost to a second cost, the second cost being less than the first price; after receiving the indication of the acceptance of the offer, selling the at least one item to the customer; after selling the at least one item to the customer, determining by the merchant server that the customer did not participate in an additional transaction with the second merchant as the customer agreed to; and in response to determining that the customer did not participate in an additional transaction with the second merchant as the customer agreed to, assessing by the merchant server a penalty against the customer.