A method and system is disclosed for building a database for use in a retail store marketing program. A reader scans a customer's check which has been received at the retail store to detect a checking account identification number. The checking account identification number provides a unique customer identification code to distinguish between a plurality of customers using a plurality of different banking institutions. A data processor includes a stored database of unique customer identification codes. Circuitry is provided for transmitting the detected unique customer identification code to a data processor. The processor is operable for comparing the unique customer identification code against the stored database and for detecting the occurrence of a match between information in the stored database and the detected unique customer identification code. When a match occurs, the processor determines if predetermined identification criteria related to said detected unique customer identification is in the stored database. If the predetermined customer identification data is found in said stored database, the processor is being operable to transmit a signal from the data processor to the location of the check scanning to indicate that the customer record is complete and that no further data is required. If an indication is provided that the predetermined identification criteria is not contained in the database, the processor is operable for generating a signal to the location of the check scanning to indicate that insufficient identification criteria exists such that steps may be initiated to input required additional identification criteria into said database. A terminal is provided for entering the additional identification criteria into the database for storage in conjunction with the unique customer identification code.