I am going to respectfully disagree. The "for sale" threads on this site are not "let the buyer beware". If you want an anonymous (and silent) experience, I would go to a site that offers that - either Facebook auctions, eBay, or whatever. If you post "for sale" on this site, feedback and commentary, as long as it is respectful and constructive, is going to be allowed. If you post a bunch of stumps in pots - describe them as such and no one will make a peep.
I would hate for someone on this site to buy a tree, have it die on him/her, and then have people say (after the fact) "oh I was worried about that but I didn't want to speak up and hurt someone's feelings".