yes, be very careful doing the negative feedback, even when it is. I followed the instructions Ebay had told me to do for a buyer who backed out, and that person put the most awful nasty feedback on mine, for no reason other than I did what Ebay told me to do, I even used the words they told me to put on the buyer who backed out. Ebay will do nothing for you when they do that, they just tell you tough luck. They should remove it, but they won't. Also, be aware that a lot of that positive feedback on those "power sellers" is from shills. They put up fake auctions and have their shills, relatives or whatever, "buy" and leave all that glowing feedback. I would never do it again, leave any negative feedback, in fact if I don't like it, and there are several things I've bought where it was weeks before they even communicated, because their nasty response is there forever on my feedback, and I did nothing wrong.
I had the same thing with tickets I bought. They obviously didn't really have them yet but sold them, and it was about 2 months. Finally when I told them that I was cancelling the sale, (because if you contact Ebay you can cancel the sale and the seller is supposed to give you your money back) they sent me, miraculously, my tickets. I think I know how some of those brokers are selling tickets, because I sold 2nd row tkts to a concert, and a broker bought them from me, and had me send them to his customer! I did not go to his web site to see what he had sold them for because I'm sure it was plenty. But I think sometimes they just take the regular people's tkts and resell them, even when they don't have them.