If you're not using some type of couponing system in your marketing efforts, you probably should be.
And if you are using one, you're probably doing it wrong.
Actually, in my opinion, most businesses do it wrong. The overriding rule of couponing is to ALWAYS ask for contact data when redeeming a coupon. If the person turning in the coupon is already a customer, verify that the contact info you have on file is correct.