we are not college professors..AND BELIEVE IT OR NOT, this is actually a SERVICE INDUSTRY. Any instructor who seriously considers themselves as a actual equal to a college professor with perhaps A PHD has a serious self inflated ego problem.Most instructors get paid minimum wage, if they are lucky..some students require more effort and time than others and many instructors are mindful enough to go out of their way to see that the student succeeds. Why not give them a tip to show appreciation and thankyou..Don't be the diver who needs addiitional help with gear assembly, help during the additional dive ,help getting in and out of the water, don't be the diver who forgot to bring their mask and an instructor/divemaster loans you theirs, and then turn around and stiff them..You want to be cheap thats fine, just tell the dm's/instructor that you do not reward/tip for excellent care and see where that gets you. You will still get taken care of , but in a standard way. Do not expect favors of additional time if you are running behind in class or have problems with setting up your gear.Many cases instructors/dm's extend themselves and are not rewarded for the additional efforts. Right now as i write this I have an instructor who took a problem student of mine on her own into the pool while the rest of class is on a lunch break. Does she not deserve a tip as a token of appreciation?