My thoughts on tipping,
I will start with a little back story on me, I became an Instructor in college, got a degree, a real job and hated it. In 2004, I moved to the beach and started working as a SCUBA Instructor for a small shop. I made less there than I had in high school clearing fences after class and on the weekends, but I loved what I was doing. To me, it was a foot in the door of an industry that I was enamored with. I was diving 7 days a week, most weeks. To supplement my income teaching, I worked the boats any chance I got.
By 2008, our education department was in full swing, and I no longer had time to work the boats. Had it not been for those generous customers, there would have been a lot of nights where I would have been hard pressed to make bills. I agree that bad service does not deserve a tip, and good service might not warrant a tip, but when in Rome, do as the Romans. If you are in a part of the world where tipping is the societal norm, please take care of your crew... it might be what allows them to eat a good meal that night, or support their family.
Also, the kind words to management help as much as the harsh ones hurt. It is good to take the time to mention when someone goes above and beyond. I have a book of notes from my students and customers that I saved from my days in the water. It softens the blows on the days when the tips aren't so good.
Just my opinion,