And now, from the real world, that of proffesional pilots and mortgage holders, I have to say that tipping is a personal choice, and I have never tried to solicit one from my passengers. I've also never refused one in 4 1/2 years of flying charters. People do it or not, it's up to them. I'm always greatful, and I never expect it (well, I try not to). I completely dissagree that it make me less of a "professional". I don't feel I'm getting tipped to fly the plane, rather, it's to handle luggage, clean up their mess, smooth out the bumps where I can, and do anything and everything I can to make their experience more enjoyable. I try to remember things that repeat customers like and cater to them. We carry forms for customers to fill out before we land in the Bahamas, and use my experience to speed the immigration process. I plan ahead to do everything possible to enhance to day for the people that pay a lot of money for our services. If they want to show me their appreciation, so be it. Some people get upset if you put yourself "above" their kindness.
Any pilot can fly the plane. Not every person can show great service.