You're telling me that the owners are cheating the customers by using "fake" lower than expected prices, because there will be the tips, dumping the pressure on the workers that are the solely individuals that will suffer a loss in case there will be no tip at all?
Great... that's even worse, and a ****** way to run a business and another reason to not give any tip when you smell a situation like this.
Stop finding excuses and justification: apply the real prices, don't cheating the customers, but especially stop abusing of your workers. This is the only correct way to run a business.
I have been discussing real prices and market forces. What are the 'real' prices in your opinion? Do you have any evidence that anyone is inflating prices and underpaying employees? If you say yes, then 100% of the dive shops in Cozumel are in on it. Because if only one shop uses 'real' prices and pays their employees correctly, then the customers and DMs will all flock to that shop causing the others to go out of business. Are you saying there's a Cozumel SCUBA trust controlling the market? You definitely should go there and open your own shop!
Edit: Let me use some made-up numbers as an example for two dive shops in the same city/location:
Dive Shop A and Dive Shop B have equivalent costs for lease, electricity, water, waste, shop equipment (incl. compressor), rental gear purchases, rental gear maintenance, labor, etc. Both of them pay their DMs with the understanding they'll earn tips (average $10/tank) so that they can keep their per-tank price to $30/tank.
Dive Shop A decides to use 'real' prices so that they can pay their DMs better. They increase their per-tank price to $40/tank and give that extra $10/tank to the DMs. Great.
Because Dive Shop B is still $30/tank and Dive Shop A is now $40/tank, a significant percentage of customers shift to Dive Shop B. Dive Shop A loses customers which means lower revenue and the threat of layoffs and/or closing the doors.
Let's say that Dive Shop A convinces Dive Shop B to also shift their model to $40/tank and pay their DMs an extra $10/tank. Now they will both lose customers to Dive Shop C through J and they will begin to lose customers to other dive sites that are now cheaper in comparison and to non-diving activities (snorkeling, parasailing, hiking, whatever) that are now cheaper in comparison.
You can say that dive shops are 'evil' by not using 'real' prices, but they can't ignore basic economics. They are small businesses probably struggling, and they either attract sufficient customers or go out of business.