I have recieved those famous "sent the check 2 weeks ago" stories. So I caught on. I said ok no problem. When you get your returned check I would like to have a copy of the back. I tell them I need a copy of the endorsment so I can file a fraud report. I explain to the customer that I never got it and never signed it and that if there is someone intercepting my mail and signing my checks that I need to press charges. This usually gets them stired up. I got a call from one lady 2 days after explaining this to her " I made a mistake, I thought I sent the check to you and I just found the bill. You can come by and pick your check up if you like." So far it has worked out. You may or may not want to try this tactic.