This brief but important letter notifies a customer that he or she has overpaid you. It can serve as a very good customer relations letter.Our document template is designed to make the process of writing an "Inform a Customer of an Overpayment" letter quick, easy, and stress-free. The salary overpayment resulted because . If we have identified an overpayment and request a refund, please mail the check along with a copy of the overpayment request letter we sent you.