I lost money with ebay a few years ago when a CPU I bought was DOA. The buyer just wasn't interested. However, ebay are supposed to have introduced some kind of assurance or insurance, it should say on thier website. I agree with jimv7, check the responses.
I'll add to the positives - only bought one item (DVD recorder) but it was good. As mentioned important that you check feedback of the seller (and probably wise to make sure that the positive feedback is when the guy is selling rather than buying).