Tipping is a practice that came from the ability to pay a non-professional performing a menial task to do it better for a little bit of extra money. If you think your instructor is subject to such circumstances I would suggest finding a new instructor instead.
Tipping divemasters (the position, not the cert. level) and boat mates is expected in the dive industry. Personally, I would be slightly insulted if someone offered me a tip as an instructor.
I would not be insulted..
usual tip in the $25. range..
Had quite a few in the $100. + area.
Best ones were the " We will fly you to our
condo on Star Island,there will be a private capt/boat there to have us complete training dives"
Or the "We will cover your expenses to join us on Grand Cayman to complete our training dives.". Took them up on it every time.
I feel a tip is a show of appreciation for the attention/care given to the client.
Never really expected but always appreciated.