Your auction ad looked just fine to me, and for such a low purchase price, the guy who left you the poor feedback should be ashamed. He obviously is inexperienced with the ebay-game to have done that without at least contacting you first. And, he opened himself up to you leaving him even worse feedback if you want to go that route. Bottom line, there is a risk when dealing with inexperienced ebayers who haven't yet learned the ebay "ropes" or understanding the lasting harm that can be done to one's feedback history. To me it appears you did nothing wrong.