It ultimately comes down to the decision of the owner of the individual shop. The agency can't force anything, but it can certainly recommend it.I am certified with NAUI, PADI, and SSI. I’ve also instructed for PADI and SSI. I’ve never felt pressured to buy gear or to push students to buy gear.
The dive shop where I worked 11 years ago had someone come in and do a week-long workshop on scuba marketing. I still have the workshop materials. He made a bunch of recommendations designed to increase the bottom line, some of which I will summarize here. His goal was to get the shop to switch to his dive agency, and when they did switch, they implemented each of the strategies I am describing below. His name was Doug McNeese, President and (then) sole owner of SSI.
- Identify specific models of gear (fins, wetsuits, BCDs, regulators, computers) on which to focus sales efforts. The more you sell of a specific model, the greater the discount you get from the maker, thus increasing your markup. My shop identified Aqualung Slingshot fins, Seaquest Balance BCDs, Atomic regulators, Atomic SS1 alternate air sources, Suunto Cobra III computers, and Henderson wetsuits, and all instructors and retail employees were to do everything they could to steer customers to those specific products.
- Instructors were to purchase (at a discount) the above products and use them whenever they were in the presence of customers, telling them that as instructors, they demand only the best, and they had personally decided that those items were the best. This was the shop's "scuba uniform," which he likened to the uniform a McDonald's emoployee would be required to wear. As a tech diver, I did not want any of those items, and everything I did use when diving could be purchased through the shop and was on display, but I could not say that. When I complained about being required to lie, I was told it wasn't lying, because those were all good items, so it was OK for customers to buy them. (The logic escaped me.)
- Instructors were to use a variety of techniques to get students to make gear purchases before they were done with (or, better yet, before they started) confined water training. A friend of mine was let go after years as an instructor because his students were not buying gear.
- There was a host of other more subtle ways to get customers to buy what was wanted; I could add many more bullets.