I would say many of the conflicts are resolved due to locks or non-editability, since most every disput begins with a mod locking the thread. Keeping things clean would not be as hard as one would imagine. Selling multiple items in one thread would not be anymore difficult, as an updating post would state the item is sold. Any confusion would only result from users not reading the whole post. By the same token, the majority of sales posts are single item issues, such as AEGs, these posts would not be adversly effected by such a policy.
Maybe you'll find someone else to help you. Maybe black mesa... THAT WAS A JOKE, ha ha, fat chance.
My Buy/Sell 1337ness rating