Lisalisa, think you have to chalk that one up to experience, when I first started buying on Ebay I naively thought people had the same standards of selling that I would have. Can you post a link, so we can all avoid this seller!
Ebayers can get a bit hungup about the negative feedback stuff - it's really best used as a last resort if things go awry. Regular sellers will be genuinely interested in how their goods are received, if only so they can do better with the next one. Trying to untangle a small-money transaction with returns and sorting out postage is usually not worth the effort - so if a wash solves the problem, that sounds a good idea - my small child always rolled in the mud in new clothes as a matter of principle, afaict :-)
I bought a bra from ebay recently, which was exactly as described, exactly what I wanted, but stank of cigarette smoke. I emailed the seller to say it had arrived (I always do this) and mentioned the smell - but made it clear I was only doing it for her info, as I knew the smell would come out in the wash. I left positive feedback, as overall I was really pleased - it had arrived really quickly as well as being exactly what I wanted. The seller actually gave me a £4 refund (on a £13 bra), which I was really pleased and surprised about. So for me, it was worth mentioning, although the only motive I had was to let her know.