I work for the USPS and if you used Express Mail to send payment, you already have a signature of receipt. You also have the original copy of the shipping label with the document number on it. That number can be looked up and it will show the time, date and signature of the person receiving the envelope. Along with that receipt, the post office uses a form PS Form 3849 that carriers use that will also have a number that will correspond to the Express Mail number and that is also a different type of receipt. The carrier will deliver the envelope, scan the Express mail number and obtain a signature on the 3849. The scanner will ask for the initial of the first name and the full last name of the person who received it. This is dowloaded in a database that can be looked up. What I would do first is to check with your local law inforcement office to see if you can file a report on your end. Then I would contact law enforcement in the city where you sent the payment and file a report there. Go to your local post office and tell them what happened and that you want to file a criminal complaint with the postal inspectors so that it will become a federal deal. Those guys are pretty good at sniffing out jerks like that. Think about it, the inspectors will enlist the carriers help in finding this guy. If this scammer does a lot of business through the mail system, his carrier will definitely know about it. Bring all your paperwork to the post office to help build the case but do it as soon as possible!!!! My condolences to you and keep us posted.