I've purchased a few items from US AudioMart and sold a half dozen or so. I've always had good luck. This includes items up to about $10K. I look at the seller's feedback and don't purchase anything that does not include decent photos and a description that sounds like it was written by someone who knows what they have. If it's an expensive item (for me, that's more than a couple thousand $), I'll arrange for a phone call and try to check out the seller if possible.
I always use Paypal for purchase, and unless I know the seller personally I don't use friends & family payment. Paypal provides pretty good protection for the buyer (less so for the seller) if there is a problem.
So far, so good.