I once had a bad experience with an ebay member called gunghotrooper. This ebay member advertised a set of wheels for a Peugeot and I won them for 99p. They wern't terribly well described and there wasn't a picture, but for that price I couldn't really complain.
The ebay member over the next few days then proceeded to give me really bad excuses as to why he (or she) couldn't sell me the item, to which I replied that I was still interested and would still collect. The ebay used then told me that he couldn't sell me the item because one of the rims had a ding in it and it was illegal. Now all I wanted was two wheels for a couple of cars I had and two to put on a car to take it to the scrapyard, so I wasn't really concerned.
I then proceeded to leave the user negative feedback and complained to ebay. After about a week of complaining that the headers wern't correct, I finally got it right an ebay said they would deal with the matter. Two weeks went by (by which time ebay had done nothing) when gunghotrooper decided to leave me negative feedback. I eventually had the feedback removed but could only do so if I agreed to have the other users negative feedback removed. Now I still insist that this ebay user is arrogant and incompetent, yet he (or she) basically got away scott free. It's users like this that really give ebay a bad name, and ebay should have taken action against the non-seller long before this happened.