Yeah, ebay sucks. As I reported in another thread, recently I had a bad experience with a seller. Result? I can't leave him a negative feedback because he will then retaliate and do the same to me despite the fact I didn't do anything wrong. So in this case the seller goes without a feedback; and it's not the first time it's happened either.
Ebay should force sellers to leave feedback first. That would be way more honest. In fact, every time I sell something I leave the feedback as soon as I receive my payment.