I've casually bought (and sold an item or two) over the years at Amibay, never had a single problem or run in with a moderator. I picked up an A1200 from a member there a while back that turned out to be a POS, but it was cheap and I didn't ask enough questions. I can see how scalping might be an issue, but in my experience, a Picasso IV is going to cost 4-500 no matter where it's being sold.
Amibench was a great place to get scammed towards the end. I've also paid for items from amiga.org members that I never received. On that note, I'm glad to have a few more regulated avenues like ebay and amibay to choose from.
