Dude,padrediver:And, uh, how have they learned this? Most posting here don't show their faces, so how do you know that they're "manufacturers"....or distributors, company reps etc, etc, etc?
Unlike yourself, I have access to their E-Mail addresses as well as their originating IPs. I know who is on my board! FWIW, when we see someone with a too nice or too harsh of review about a piece of gear (or resort, or whatever) we check both to see just who we are dealing with. We have exposed many a charlatan this way and it usually comes after a user's BS-O-Meter goes off.
Also, we have the creme d' la creme on our board. These guys and gals are early adopters who see things from every angle. You might fool them for a tiny bit, but don't count on it... and definitely don't try to do it long term.