AP

Should you tip, even if service is bad?

You know the guy deserves a tip, but you don't know how much you should leave.

Talk about feeling like a rube.

Need to know more about tipping?

"Tipping is an unwritten, implicit contract," explained University of Texas at Arlington economics professor Mike Ward.

That contract entitles you to good service—and obligates you to pay for it. But tipping is only partly about economics; it's also about psychology.

"The cost of overpaying by a buck or two is less than the cost of someone treating you poorly, because they found out that you're not going to pay them what they're expecting," Ward said.

So what would an employee at Cup 'a Joe in Arlington consider a generous gratuity for a $3.50 mocha? "Good tip on this would be about a dollar," the barista said. "You could give 50 cents; that's a pretty good tip."

Actually, experts say counter employees—like the guy who makes your coffee, or the place where you you pick up pizza—require no tip at all. At Cup 'a Joe, that's common knowledge.

"If people don't put a dollar in there, it's not really a big deal," the coffee shop employee told us.

But there are places you definitely should tip. A hotel is a good example. Give the doorman a dollar if he hails you a cab and $1 for every bag he helps you with.

The housekeeper gets $2 a day. The concierge, $5 for a dinner reservation.

If you're headed to dinner in a cab, what kind of tip does the cabbie expect?

"Not much," said cab driver Zoran Jajcania—at least for a short trip. "If you are going long fare, you will get paid well anyway."

Actually, you should tip a taxi driver 15 to 20 percent of the fare, and that goes to someone you'll likely never see again.

In other situations—like a visit to the hairdresser—you're looking to build a relationship. Listen up ladies: You should leave a $1 to $3 perk for a basic shampoo. The stylist gets 15 to 20 percent, even if he or she is the shopowner.

"Most people don't like to have the reputation of being a cheapskate or a miser," Ward said. "They want to be thought of as being generous and so forth."

In that spirit, here are a few more guidelines:

• Restaurants: 15 to 20 percent

• Valet parking: $2.

• Pizza to your door: 5 to 10 percent.

• Give your babysitter a nice holiday tip worth about one week's wage.

E-mail dschechter@wfaa.com