The first guy I talked to tried to get me into a bidding war but I didn't want to go higher than 4 keys per copy as I've spent enough over the past couple of weeks, haha. Fortunately, though, the other guy came online quickly thereafter and he was receptive to my offer.
Since the game uses GFWL (i.e. there are no retail keys) and only went on sale once in a blue moon it shouldn't take long for current copies to dry up.