Well my Mom and Pop dealer is where I get my air at my local LDS.. I hope he doesn't go away. But he's "converted" and sells online now. In fact, he's the one who started this thread.
But I see your concerns. Many mom-n-pop dealers have gone under in the recent past. In the last 8 years we've had almost 10 local dive shops go out of business that are within an about one hour drive of me. Most of them were poorly managed and were a poor excuse for a retail establishment whether they were a dive shop or not. They sealed the fate of their own demise.
Yes it is sad that they lie to their dealers. These manufacturers also lie to their customers.
While un-restricted advertised price might be better for the dive consumer, I think it'll turn the dive industry into a no customer service Walmart type industry. The Local Dive Shops will really suffer then. Many of the mom and pop shops that are barely keeping alive, either on their own or with internet sales, will suffer. Why? becuase the hugher volume discounters that do nothing but push a box will '*****' up the market even more. Then we will have trouble finding dive shops open to get air fills from.....
Take for example the Tusa X-Pert Zoom fin. It's a good example because it's a very popular fin and is highly rated in reviews. List price for it is something like $175 to $189 bucks. Do a google search on it and you'll have a hard time finding it for under $129. Why? because MAP for it is $129. Even Leisure Pro sells it for $129. But I've seen it for sale many times for $99 bucks, but typicallynever "nationally advertised" for that, since that's not allowed per dealer agreement. I've even been in Divers Direct before and they had it for $99 on sale, but on their web site that same day it was still $129.
As odd as that is.... I really don't know a solution that won't turn the market into a worse market than it is now.