Horseshit.
I waited tables for several years. Black customers were, on average, nicer than white ones. The worst tables I had were obviously ignorant, loudly demanding, entitled white rednecks. They also tipped the worst - even with the snotty after-church crowd on Sunday (also mostly white).
You're not nearly as good at concealing your racism as you's like to believe. Either you're judging Black customers on a different scale or they see right through to your prejudice.