Unfortunately, Armslist seems to accumulate more scammers than other gun auction / sales websites. Sorry for your loss. It's a tough world out there. A few times I sweated the return of my certified payment on a very respectable (pre-internet) publication.
Some people use other forums, like this one and others similar, with a brand new user name asking about a nice or scarce piece then the offers just start rolling in on an item he / she does not have but rather only "lifted" pictures form someplace else.
I think this crime is Federal, scams that span to different States, and it's mail fraud as well as other illegalities.
One excuse was, even though I was first to call to accept his ask price, someone called afterward to offer him more money. He thought that was perfectly OK but I did get my cashier's check back about 10 days later in a US First Class envelope when I sent it to him Overnight. I truly sweated that one it was for $7K.
Another time, an old timer in Idaho, sold me what was to be (no pictures back then, just a text classified ad type description), an original 98% New Model 3 Australian, for $2,500.00 which was the correct price and a tick more for one if it was as described. After if was delivered, it was clearly refinished even over pits, with the hammer, trigger and trigger guard nickel-ed, too.
I called him to return it but before I could explain he told me a contractor was putting a new porch on his house with the money. Afterward he said I could return it and he'd get the money together, somehow. I decided to keep it instead of risk loosing the money and the gun, selling it 10 years later, presenting it for exactly what it was (a refinished NM3 Australian) for the same money I paid.
I suppose all of us, at one time or another, got blatantly scammed, not including the times we may have bought into a tall tale and plopped down way too much money based upon that "tall tale".