I've said it before and I'll say it again...I don't even bother with the "bribe". I just ask very politely "is there a better room available?" 9 times out of 10 this works. I've been upgraded to oceanfront rooms, Club level rooms, and corner suites. Obviously the success depends on the hotel, the season, what other events (i.e., conferences) they are hosting. But I find the direct approach works fine. I will say that, when I've discovered that the upgrade was to a particularly great room, I have gone back to the clerk and tipped anywhere from $25 to $50.