En español  |  The emergency road service guy showed up in record time to recover the keys you left in your locked running car. Your first instinct is to graciously shake his hand, then pull him in for a bear hug, but a tip would be far less embarrassing. But, wait. Do you tip road service folks? If you do, how much?

Tipping is a very old practice, but it remains a source of debate and confusion for many. At a restaurant, you don't think twice about tipping the waitstaff. But you might ignore a tip jar on the counter at a deli. And the idea of giving the cable guy any extra money may seem ludicrous, but the fact is that it isn't unheard of.

Etiquette pros offer advice on whom you should tip, how much and when. — Getty Images

"Tipping is important. There are so many services where people aren't even paid minimum wage," says Debby Mayne, etiquette guide for the resource website About.com. "The pizza delivery guy is out there braving the elements. There's a reason why you didn't go get that pizza yourself."

So when you find yourself face to face with one of the following service providers, handle your gratitude with grace by following these "tips."

Food server

For a full-service, sit-down meal, 15 to 20 percent of the pretax bill is customary. At a buffet, leave a 10 percent tip. Just picking up a sandwich or a decaf latte from the counter? Tip at least 10 percent.

Exterminator

Getting rid of pesky critters in your home will cost you. But the peace of mind may be worth slipping a little extra to the bug guy. Mayne says exterminators generally don't expect tips. "But if the person does something extra, such as treat an area more heavily than normal or move furniture, you may want to tip $5 to $10. Holiday tipping of $20 or a restaurant gift card is always appreciated," Mayne says.

Valet parking personnel

When your car is returned to you, it's appropriate to tip the valet $2 to $5.

Hairstylist/barber

Stylists and barbers should be tipped a minimum of 15 to 20 percent of the service, and that tip can be split among others who assisted (for example, the shampoo person and colorist). Apply the same value to manicures, pedicures, massages and the like. Think the owner of the salon shouldn't be tipped? Turns out that's an old tradition. Owners today appreciate and will accept 15 to 20 percent.

Maid

At a hotel, you're expected to leave a little something for maid service, based on how many days you stayed. But what about at home? Tipping a house cleaner who's employed not by you but by a cleaning service is optional. If you feel so inclined, 10 to 15 percent is acceptable. At holiday time, or if you're particularly impressed by a job (the gunk was cleaned from all your liquid soap dispensers), increase it, but by no more than $20.

Generally you wouldn't tip a cleaner you hired directly, except perhaps for the holidays.

Next: What are the top 3 rules for tipping? »