It shouldn't be tolerated, it costs sales because if you are quickly scanning the new sales threads, a lot of people will not click on a post with replies assuming that it's likely sold.
Things have been a little slower lately, but when there are a few dozen new classifieds posted and you're quickly scanning them, I know I am not the only person that won't bother clicking on a thread for something I might only have mild interest in if I see there's been replies.
If it's something I am specifically looking for, I will probably still check, but there have been many times where I have a little bit of interest in a post and ended up picking up the knife, but would never have clicked on it if I saw it already had replies.
When you only have 10 or 15 minutes to spare and there are a lot of posts on a variety of different subforums, I don't bother looking at threads that have replies.
On the up side, if you are a seller and make it absolutely clear that you do not want ANY POSTS except "I'LL TAKE IT", most people respect that. That includes any legitimate questions.
Is there a way to delete these unwanted comments? I forget if you can delete them yourself or if you have to ask a mod.
Either way you it's unacceptable, and it's no secret that some people will purposely post a comment to deter other buyers while they consider whether or not to buy the knife.