Abstract: A computer system is located at a retail premises for executing a point of sale transaction comprising: a point of sale terminal having an interface for receiving product data from at least one product purchased by a customer, the product data including a first price for the product; a processor arranged to execute a computer program which receives from the point of sale terminal first price data including at least said first price and second price data pertaining to the product, the second price data being from a remote source, compares the first price data with the second price data and issues a voucher request based on the comparison of the first and second price data; and a voucher issuing unit arranged to receive the voucher request and to automatically provide a voucher to the customer responsive to the voucher request.