I'll add this.

Many establishments, including restaurants, have some kind of notice to the effect of:

"We reserve the right to refuse service to any customer."

So long as that refusal is not based on legally protected characteristics like race, religion, national origen, disabilities, the place can refuse service.

(Note: By national origen I do not mean nationality. Refusing to serve people with Italian-sounding last names is discrimination by national origen, and is illegal. Refusing to serve people with Italian citizenship is discrimination by nationality and is legal.)

Thus: If the restaurant manager gets the impression that you are a poor tipper, that manager is perfectly within his/her rights to refuse service to you, based on a poor tipper profile. If, for example, the restaurant manager notices that Martians are usually poor tippers, and when challenged the Martians say "We don't tip at home, Earthling, why tip here?", the restaurant manager can refuse service to anyone who is Martian. (He cannot refuse service just based on a Martian-sounding last name or green skin.)

Furthermore, a good manager in a good restaurant with a good staff will do exactly that, just to protect the staff. Why fill up tables with notorious bad tippers when, instead, you can fill up tables with decent tippers and keep your staff happy?

Or, if business is slower, why not stick the bad tipping Martians at the table next to the restrooms and just give them indifferent service? Who cares? They won't tip even if you knock yourself out for them. Save your good tables and better service for Earthlings who do know how to tip.