I am pretty sure that every instructor who works for a dive shop has some sort of understanding about using the gear that the dive shop sells, and I am sure that every one of them gets a discount on such purchases. Some shops go well beyond that, though.
Just before the shop where I first worked decided to switch agencies, they had an on-site week-long workshop conducted by the President and owner of the agency to which they soon switched. I attended it. It was all about how to sell equipment. One of his key points is that all instructors had to understand that they were primarily there to sell equipment. One aspect of that was requiring them to own and use their "instructor uniform" whenever they were in contact with customers. He likened it to the uniform worn by employees at fast food restaurants. The shop was to determine which specific pieces of equipment they wanted customers to buy the most, and they would require their instructors to purchase (at a good discount) and use those specific items. They were to tell their students that they selected those items for their personal use because as instructors, they knew what the best equipment was and that is what they wanted to use. With the exception of the wet suit, I would not have purchased and used a single item that the shop eventually required instructors to purchase, but I left the shop before I had to buy that gear and lie to my students about having purchased it of my own free will. (BTW, the shop sold all the gear I really did own and use, but it was not the gear they wanted the students to buy most, the ones that provided the best profit margins.)