it depnds on the part. I've bought a couple of things and had no problems... but then other have gotten burned... Like The general said... all the crazies (OCr's) sell their components to upgrade... if you do buy I would suggest something form one of the ebay stores that will sell it new...
I'm getting a new pc build [most parts] off ebay, and have ordered them. Here's a few tips you may find useful..
- Find Items which are new and still in package [ Obvious but some people miss this ]
- Look at their feedback, if it's a high number [over 100] and it's 99% - 100%, then there's a low possibility they're lying on anything [ i.e condition of the item]