$20 Trick is when people think that they can BRIBE the hotel front desk at a Vegas (or any hotel) for an upgraded room. This is not a trick but in fact a BRIBE.
Believe it or not you can ask nicely and if they have availability they will upgrade you for free.
Hotel clerks don’t have a magic “check box” that says “$20 Trick” and they click on it and upgraded rooms magically appear.
I did the $20 trick at Circus Circus and I got the clown deluxe penthouse suite with fountain views.