I believe myself to be a master of the 20 dollar tip trick at many locations. I use to always get what I wanted. Well my last trip to Vegas I was denied at every try.
I believe as much as the workers want the 20 dollar tip, some are afraid of losing their jobs.

One example is I always rent an economy car and for 20 bucks would get a Chrysler Turbo 300. This worked trip after trip. When the girl turned me down, I said you sure. She said I would really love to, but I just can't anymore.

Barry