When black customers don’t tip, is that because of racism or because they are cheap?
Option three: both.
Like most, I started my working career way back in the late 70's and early 80's working in food service. I am NOT stereo-typing when I say most black customers either don't tip at all, or are very poor tippers when they do tip.
At that point, things become self-fulfilling prophecies. I've also been in restaurant situations where wait staff didn't want to wait on blacks that came into a restaurant because they knew no matter what level of service they provided, they'd either get no, or a very poor tip.
The result: they provided poor service and received no or a very low tip.
Very glad that my time working in that sector as I started out my working career was relatively short. Learned alot about people.