If someone is asking if their 5 pound pack is too heavy, they actually want your opinion. It's okay to say it's fine, but it's also ok to say "oh my god that's 4.5 pounds too heavy!" If the poster didn't want an opinion, they wouldn't ask on a public forum.

That said, a lot of us (myself included) are guilty of offering unsolicited advice. Most of us mean well, and I think this board is pretty tame when it comes to trolling. Easiest thing to do is ignore it, an unanswered troll is just a dead topic that will be forgotten after a week (the default search criteria.)