I bought a tank online, then called a local LDS about having the valve installed. The conversation started with him saying "take it to another shop, you don't know much about tanks". After I read him every label on the tank, he agreed (very reluctantly) that a new tank that was hydro'ed and inspected at the factory in 2/06 and never used would PROBABLY not have any internal damage that would show up in a visual. I wish he would've just said "Since you bought it online and I didn't make any money, I'm going to charge you for a visual." I can respect honesty.
I guess I learned that some DMs don't like it when a diver can read, rather than just listen to what THEY say.
The next guy said "Huh" when I said DIR, so I said "cave or tech divers" and he said "I don't care how many times you wrap your hose around your neck, it's not going to save you.". Yeah, OK, I'm supposed to feel confident buying gear from him? He's clearly only familiar with gear he sells (not really, but that's another story), so what if the gear he sells isn't right for my purposes? (Nonsense!!!)
My conclusion? If your instructor says he has 30 years of experience, expect to get a very thorough training in 30 year-old techniques. (Okay, a little harsh, but there have been advances in techniques and equipment which MIGHT interest a new diver.)
In your case, I suspect the DM saw a diver (you) with a robust, streamlined setup that was superior (and overall cheaper) to anything he sold. If he let those other divers leave without bashing your gear, his customers may start looking elsewhere.
You should rename your thread:
"I'd tell you about my BP/W, but then I'd have to kill you."