Notwithstanding poor or mediocre service, tipping is customary in this country. You can write if off as a business expense if you’re really that cheap. If I were another hotel guest on a van with a bunch of people wearing their corporate uniforms (in this case a flight crew) and they didn’t tip, I would sure as hell judge their company and their profession based on that. Keep in mind you never know who’s watching your behavior. Tipping is precisely one of the things per diem is for. I’ve worked for tips in my life and it sucks. You can say “Well get another job then.” I did. Now apparently I have to deal with coworkers not having the simple courtesy to give a van driver making close to minimum wage $1.