I've never had a problem with ebay, I haven't bought anything from a private seller though I've only bought stuff from companies like procarparts.com, you can find their stuff on ebay for cheaper than their site.
I have made quite a few purchases on eBay both from private sellers and pros. I have not had many bad experiences as I always check out the sellers feedback and read what other buyers are saying about them. It helps alot. When in doubt, ask questions. I have bought everything from a GPS to xmas gifts and have not been stung yet. And saved a crap load of cash as well. Hope you're experience turns out as well as all of mine have. Chuck.