I used two operators in Cozumel.
One was Aldora. Was treated OK in most respects, very good in another.
The other dive operator was someone else. I paid them a lot of money for a course they claimed they were certified to teach, took the course, and then once I got home, was told they were not certified to teach it after all, and was offered a refund, which I accepted - but they refund never materialized. After months of hounding them, I finally gave up. Guy seemed like a real nice guy - seemed really sorry about the situation, but in the end, the money never appeared - which esp sucks given I bought an overpriced SMB from them when I could have just got it on-line - but since I had already inquired (in a serious fashion), I felt morally obligated to buy it from them.
Now - you can decide for yourselves who the sleaze is.