I used to work as a waiter in a restaurant in a small city that is a state capital, home to one of the service academies, and is about 300 years old, thus a big tourist destination. Therefore, I served a lot of politicians, lobbyists, etc. who were mainly vain, with big ole egos. Most were experienced restaurant goers, and therefore, very demanding, but very appreciative of good service also. They tipped well, but you earned every penny of it. Military brass was a mixed bag. Tourists were very friendly and tipped lousy.
It was my experience that blacks are indeed very bad tippers, however, the best tip I ever got was from a young black minister who brought in about 15 of his elderly church members for Sunday brunch.
Waiting tables is like any other business. You have to concentrate on doing your job well ALL the time. If you get bad customers who don't tip you just have to forget about it and go on.
Here's my general experience. Blacks are terrible tippers. Indians are worse - in fact, I have noticed that most Indian restaurants make a 15 percent tip mandatory. Yuppies are great tippers. Men on dates are typically great tippers. Women who eat alone or with their women friends are usually bad tippers (its as if guys are always buying their meals, so they don't understand tipping). The elderly are a total crapshoot, but they tend to look at 15 percent as the maximum. Previous waiters are the absolute best customers!
I was waiter during high-school and college...
I also sold cars. Blacks are the most profitable. Married couples tend to do a lot of research and yield little profit. I don't know how any Indians have cars, because they are completely unreasonable. They will offer 10k for a brand new car worth 30k. They think they are being generous when they up their offer to 11k and won't leave when you ask them to (because they completely waste your time).