Mine has a tiny, and I mean tiny, practically un-noticeable mark at the bottom on the bezel/edge. I can only see if I really look for it, half the time I forget it's there because I look and can't see it, then if I angle it correctly under light I can spot it.
I don't care about it. My iPad has practically zero backlight bleed, no dead pixels, the screen isn't yellow and there's not a mark on it anywhere else. I could exchange it but why bother? It's not worth the effort, if I do re-sell it on later then it's probably going to have another knock or two, not that anybody in the real world is all that OCD, certainly not people looking for second hand iPads.