Thanks for the support. Some may (or may not) know I'm a Mod over at FBBO, and I DON'T allow that kind of thing to go on over there. All it does is cause problems, and I won't stand for it. It shouldn't be tolerated here either.
I agree! Unless someone has specifically posted a request for criticism, I'd say don't do it. Put yourself in the seller's place. Then remember that just because you have an opinion doesn't mean anyone else wants to hear it. There are a whole lot of ways to share your "knowledge" without destroying someone else's chances to sell something. It's only commom courtesy.