... when they accept the offer after we communicate via audiogon, phone or email, I have a pretty good idea about the person I'm dealing with."
I agree with you on this, and I make it clear that they are there to confirm the equipment works and appears as represented, not for a test drive to see if they like it. I insist on a phone call before I allow them to pick up an item in person. If the buyer start to balk at that in the least I find another buyer. Also, you should only accept cash if they pick up the item.