The best thing to do in this case is to wait until the last day you can leave feedback and then post the negative. Hopefully the seller won't be quick enough on the draw to fire back a un-earned negative.
I got my only negative from a seller that stole my $$$. This shows you how much eBay favors the sellers. I've given 4-5 negatives on my 200 or so transactions. All were "earned" by the sellers. When I sell, I post positive feedback when I recieve payment. I think eBay could change it so the seller feedback deadline is 30 days, and the buyer is 45 days. That way there is no chance for a retalitary negative.
