I've bought many toys on eBay and I've been almost entirely happy with the experiences. My favorite thing about eBay is being able to see a user's feedback before deciding whether to do business with them. I only do business with users who have plenty of feedback, and a perfect, or near-perfect, score. That would be my advice for anyone.
My only disappointments were cheap BDSM toys when we were still figuring out what we liked. The only think I don't like about buying adult items on eBay is that it's a bit clunky navigating to the adult section, and then having to go through a second log-in process. But for items Eden doesn't carry, it's worth it, in my experience.
My biggest score so far was getting the ASLAN Vegan Jaguar harness, new, for $30, including shipping. This was right after Eden stopped carrying it. It's one of our favorite harnesses.