I've had no issues with Amibay itself. I just dont trust all Amiga buyers anymore. Some are good, but there are scammers out there. Especially if you have a perfectly working motherboard with picture proof it works, then buyer says "oh it doesnt work" and files a Paypal claim. Good thing for me, I had $0 in Paypal and closed my acct. :-)
EDIT: On Amibay... I think the site is pretty good, rules are fine. I'd go there before I hit ebay.