Many regular visitors to Las Vegas see the $20 trick as their first real gamble when they arrive in Las Vegas. The $20 trick works at your hotel as you are checking in, when the hotel desk employee for you credit/debit card and identification slip the $20 bill between the two items; As you are handing the items over ask if there is any free upgrades, many times the employee will start typing away looking for an upgrade for you.
If their boss is nearby they might just hand the money back but many times they will look for upgrades which could include things such as a Strip view, pool view or even being upgraded from a regular room to a suite. If the desk employee finds an upgrade they will tell you and, if you agree then keep the $20, if it’s during the week or non peak time you will have more of a chance getting an upgrade.
This doesn’t work every time which makes it a gamble but it does work a lot and is worth a try. I wouldn’t recommend trying this at a motel because being upgraded to the room nearest the ice machine might not be worth the $20.