I haven't had a bad transaction on ebay yet. People are always leery of car parts on ebay, but there are good deals to be had. Just bought a full set of brakes and front control arms for my wifes car and paid under $200 bucks. Fun fact is, the control arms are the same as some parts stores just rebranded and the brake parts are the same. Pads are the same as some house brands, just unmarked (Bendix, which are decent economy pads) and the rotors are easily traced and are good quality. Even the cheap starters are worth it. Paid $40 for a starter for her car, only thing I had to do was to put the connector from the old starter solenoid onto the new one. No big deal. Been working fine and I'd do it again.
Also got my Blade HQ Shaman on the Bay, and it wasn't ridiculously overpriced (although it was a little more than I wanted to pay). Seller had it up for auction or best offer, and we haggled until we were both satisfied.
Did have one mix up. I wanted a Kershaw Injection 3.5, found one and ordered it. I got a Kershaw Starter with the playing cards. Contacted the seller and they refunded me and told me to keep the knife. Ordered an Injection from someone else and it was a great transaction. Still haven't opened that Starter knife...LOL
Just have to be careful, but I can see how problems can happen. I've either been lucky or just diligent.