Sometimes those rules are honored, but sometimes they're broken.
When economic times are tough, consumers spend less, and that often means cutting back on gratuities.
"The dine and dash is back, and although they're paying the bill, they're not leaving any tips," says Eyring.
Coast to coast, servers are feeling the squeeze with fewer customers, smaller orders, and less tips.
"People who would tip you a little bit more like 15 to 20 percent are usually going for the 10 percent, 15 percent," says Jonathan Mancipe, a server at Bodega Restaurant.
"For every 50 bucks you spend, you should leave your waiter 10. I'm seeing six and five," says Tom, a server at a different restaurant.
So is this excusable behavior in a bad economy?
"It's just like stealing. I mean it's just like not paying the bill, it's part of that; gratuity is part of the meal," says Eyring.
The tip is a big part of a server's income. Usually, much of a waiter's minimum wage salary goes to taxes. Many of them share their tips with food runners and bartenders. Experts say if tight times have you tipping less, chew on this advice: order less, or take advantage of specials.
"If you're going to dine out and go to nice restaurants, then you pay the tip," says Eyring.
So how should you tip if the service is poor? Experts say that's the only time you consider giving slightly less, maybe 15 percent instead of 20 percent. However, before lowering the gratuity, speak to a manager first.