I have certainly seen other LDS turn a cold shoulder to people who buy online. I think thats short-sighted, but human nature. What would really ticks me off is when I spend time talking with prospects, showing them the strengths and weaknesses of various products, allow them to go in the pool with the gear to try it out and THEN they go buy online.
I even had one come back later and try to get me to help address a problem with reg he bought from LP. I politely told him that I would be happy to, at $50/hr minimum 1 hour and that had he purchased it here, I would have been happy to include that service in the price of the reg.
As a retailer you're entitled to set whatever differential policies you like.
But, if you don't do the same thing in terms of charges to a customer who buys a reg across town (or in Cozumel, for example, after losing one for some reason) as to the person who buys from LP, then you can expect that educated and intelligent consumers will conclude that you "hate" a particular seller or group of sellers, and intend to hurt them.
Since those sellers are pretty clearly acting in the best interest of the consumer (with their lower prices), don't be surprised if those same educated consumers decide that you are out to hurt THEM, conclude that nothing you say or do can possibly be in their best interest, and that EVERYTHING you do suddenly becomes suspect - including your air quality and instruction.
After all, fair is fair, right?
In the end a "fair" mark-up is what the market will pay. Where it becomes less then fair, and treads awfully close to the line of fraud, is when you start trying to support your pricing with outright lies about the lower-cost sellers (such as "you have no warranty" - false - "that's counterfeit gear" - false, etc) in order to scare or pressure people into buying from you.
Again, the proper response to that from consumers is, IMHO, to decide that whatever that seller is offering is equally suspect.
Poof - there goes your business.