I have to disagree with you on this point - at least from my experience with the particular dive shop that I used. We have been there twice now with Blue Angel dive shop and I never once felt that they were just trying to get our money. The divemasters always seem to be friendly and enthusiastic about finding neat things under water, and are always there to help setup your gear, etc.
I'd say many of the shops on Coz have a similar good attitude - just check the regional forum under Cozumel on Scubaboard. Dive with Martin, Living Underwater, Blue XT Sea, etc. are highly regarded on that forum and I think they might change your mind about that.
I'll go further and say that the service in the restaurants is also better than most restaurants here in Colorado. They genuinely seem to want to please.
YMMV!