Save one, I've had very pleasant, fair experiences. Fortunately the exception wasn't a huge loss. Sent me the wrong zoom ring (my fault for not checking as soon as I got it) & two triggerfish slave eyes (both dead: it's a permanent battery). Again I didn't test immediately & it didn't occur to me to confirm old or new model. Perhaps if I'd done my due diligence he would've been responsive. Also research the pay pal protections, they are reassuring.
Finally, I operate on the sense that we're part of a community that has a commonality of love & respect for the water that hopefully extends to our co enthusiasts. It's a presumption I'm willing to go on. That should distinguish us from used car salesman…