3. Bad Service Pays
Research has shown that people tend to tip even when the service is terrible. Case in point—the Iowa couple who recently made news for leaving a $100 tip and a sympathetic note on a $66 bill, despite the bad service.

4. Taxis, Too!
When it comes to tip guidelines, remember that taxi drivers also fall into the category of workers who rely on gratuities to stay above water—20% is customary. When in doubt, Emily Post is always the definitive guide to all things etiquette.