If I were to require my DM's and DMC's to only use gear that I sell when they already have a full kit the decent and moral thing to do is to provide it for them. If it's a BC or basic reg set they are not going to buy it. I'm going to give it to them. To make them buy it, especially DMC's who are paying for a course, NOT GETTING PAID TO BE A BILLBOARD FOR THE SHOP, there is no incentive or justification in making you buy another full set of gear. If the shop wants you in a Bubba Bob Super Deluxe BC then they should have one for you to use at no charge. Otherwise reduce the cost of the DM course.
If the DMC has their own gear and the shop is making them use rental gear I hope to hell they are not charging them the rental fee. That's just ignorant.
I like Abyss Scuba's approach. Wow, we actually agree on something business wise

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But seriously, if the brand you sell is not good enough to sell itself or you are not salesman enough to sell it because your DM's or Instructors are using something different that ought to tell you something. Like maybe prices too high, gear not what the student wants, or it just doesn't meet their needs. In any case most new divers wouldn't know what brand the instructor was using. Especially when in some classes they see so little of him/her in the pool. Or they are so busy trying to digest all the info that is being crammed down their throats in a short period of time that they aren't even paying attention to the labels.
As for instructors needing to be in the same gear as students? Horse pucky. A good instructor can quickly explain and demo the differences in gear configurations and not miss a beat. I often switch between a plate and wing, back inflate, and jacket (and usually all different brands. Only one of which I sell).
A 5 - 10 minute poolside brief (required by my agency anyway) followed by a clear demo and I've yet to have a student get confused. The similar gear thing is another myth perpetuated to sell the high profit margin goods.
And what really frosts me is when I see or hear of rescue classes being taught that way. Nuts. I had everything from integrated octos and basic jackets to a guy in a drysuit and full north Atlantic wreck gear with doubles and gauge set up I had never seen in my last rescue class. And the next one will have someone in sidemount. I'm getting my SM rig next week

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