You can't really judge who will be a good tipper and who will be a poor tipper. It's usually those who have had all the advantages and never bother to think about what someone elses life is like or can't be bothered to find out what wages are for a profession, who go off and leave 10% or nothing at all. They can't be bothered with the fact that the woman who just ran her feet off taking care of them has 3 kids at home and she refuses to take welfare.
Some are ignorant of the facts, some are cheap, and some are just tacky, thoughtless people. Mostly it's liberals.
Might have been true in the past, but now the government expects / demands that reported tips are at least (my guess) 12%.