I've never tried that and don't think I ever would. A friend did tell me something that works for her though and I've tried it also and had good luck. You reserve your room then show up late. Let's say check in is 3:00, you show up at 7:00 or 8:00 say after a nice dinner. If the hotel is busy they sometimes will fill the less expensive rooms and when you check in they will give you an upgrade. I would trust this more than trying to bribe a hotel clerk with a $20 and you have nothing to lose.
He done a fine job for his clients in any event!! fisherman100