The mail fraud charge, not really. If it were a large amount, maybe. It has been shown time and time again on the different boards that the USPS will do nothing to these scammers. Many fellows have contacted the post master general and gotten no results, just a run around and it'll be checked into.
Paypal is your best form of protection from scammers. If a seller will not accept paypal, I will not trade with them. It just takes a few minutes to get it setup. If you use a check card or credit card as your paypal account you also have double protection from what ever company, such as visa.