Shamelessly stolen from Incar an Admin on a sister forum Sig Talk:
No credit cards, and only electronic cash payment? Most likely a scam. Ask them for their FFL number. IF they give you one, look it up on FFLeZCheck 3.1.2 - Federal Firearms License Search (atf.gov) . Not there? Guess what - not legit. Is it there? Great look it up Federal Firearms Listings | Bureau of Alcohol, Tobacco, Firearms and Explosives (atf.gov) , when you find it (it's easy), get the phone number from the lookup and give them a call - verify that is who you are doing business with. If they won't provide you a number, then avoid them at all costs. No legitimate FFL will refuse to give you the number to verify on EZ Check.