Proof of purchase is often required for and manufacturer rebates as evidence that the customer purchased the product. When multiple purchases are required to redeem these rewards, it is referred to as a premium incentive or collector mechanic.
Traditional proof of purchase systems required the consumer to send some portion of the packaging, as defined by the product's manufacturer, or the sales invoice.
Unique codes printed on packaging are increasingly used as a mechanism for proof of purchase. Consumers can submit the code electronically for validation against a central database, thus establishing proof of purchase. Such systems allow manufacturers to develop a direct relationship with the consumer, for use in short term sales promotions, loyalty systems and collection and profiling of consumer data.
Stores which accept returns may require proof of purchase, often in the form of a receipt.
Some major retailers may accept reference numbers, usually allocated on invoices and confirmation emails as proof of purchase.