The RC Heli site I frequent has a feedback system where only the buyer can leave feedback....positive, negative, neutral and a comment. There has to be a link to the sale......like to where the item was advertised on the site........all feedback can be reviewed and edited by the mods of the site. Have a bad deal, report negative feedback on it. They also have a forum for scammers, rip offs, and stolen stuff. It's to alert people of a shady transaction. The feedback system if for VBulletin, but I'm sure someone can port it over to Xenforo or someone can write a mod for it. It works very well though. Here's a link to my feedback page:
http://www.helifreak.com/itrader.php?u=163699
I've been a forum owner for close to 15 years and have done much mod/administrative work.
I think deleting posts is just wrong! Moving that particular post to a hidden forum is one thing, but we never deleted. If someone is going to act like an ass, well then leave it for all to see. If it's that bad, move it to an archive forum, and discipline as necessary (week vacation, month, ect.) No mod or admin should be editing any other one's post. That's just wrong and bad for the site.