Accordingly some embodiments, a merchant server receives an indication of acceptance by a customer of an offer for a subsidy from a second merchant of a purchase of at least one item from a first merchant. The customer agrees to participate in an additional transaction with the second merchant in exchange for having the subsidy applied against the purchase from the first merchant. In one embodiment, after selling the at least one item to the customer, the merchant server determines that the customer did not participate in an additional transaction with the second merchant as the customer agreed to, and assesses a penalty against the customer.