At the shop I last worked, the discounts on gear came directly from the manufacturers, NOT from the shop itself. There was a section in the front of each catalog that explained the program offered to dive pros by the manufacturer. We were able to order gear directly from the manufacturer, pay them directly, and it was delivered to the shop (with my name on the package.) It was a win-win-win: we got large discounts, the manufacturer got the best advertising (it was amazing how many of my students would buy the same reg I used...) and the shop sold the gear to students.
But when I would travel I would talk to other instructors about the manufacturer discounts, and many of them had no idea it existed. Seems like some shop owners would rather sell gear to their instructors instead of allowing them to benefit from the manufacturers' discount programs.
I was also paid per student, in US dollars, by the shop for teaching classes.