It's not just on audiogon. Scammers are prevalent everywhere these days. I'm from the IT industry and am surprised at how brazen they are becoming. Both from a technology perspective as well as social engineering. I do my due diligence and haven't been burned yet but....it's a new world out there.
If I have any concern whatsoever I do a phone call with the buyer or seller. I ask for emails, not just PM's. I only use paypal. I look up clients address. I do anything necessary to be comfortable before the deal takes place. If I can't trace a potential sale to a real person, I'm done. And if I don't like what I'm seeing, or even think I smell a small rat, I'm done. If a buyer or seller have no feedback, I'm done.
You really need to be ready to say no these days.