I have few qualms about dealers posting on forums. It’s up to me whether I find their posts useful or not.
That said, and especially having been back in the speaker market again over the past few years, I can not remember a dealer who has ever offered me advice of any worth. Even the nicest most well-meaning dealers.
First, they have something to sell, so their view is inevitably skewed towards those products.
Second...I don’t care how much experience they’ve had with gear they sell and others. They’ve come to their own conclusions and those are not my conclusions. When they are talking about gear I know and have heard, I often don’t agree with their take on it, or if I do then they haven’t added anything to my own. (Even in the speaker forum a certain dealer-in-question who has posted a description of a speaker I've auditioned, and it didn't match what I heard at all. I have no reason to rely on such accounts).
When I go gear shopping I’ve done my homework and I bring a lifetime of audiophile experience in knowing what I’m looking for. I don’t need a dealer to say a darned thing; I just need to hear the gear for myself. Nothing the dealer says matters at all if the gear doesn’t meet my standards and criteria.