This would not prevent account sales, as one could easily do it in private or on a external site. I don't see it being a bannable offense anytime soon (even though I would not mind it).
I guess I don't understand this argument. It seems more like clinging to the status quo that, at least with respect to account sales, is broken. The sales may very well take place outside this forum but by banning them here it certainly makes it more difficult, for buyers and sellers. This is common to a lot of forums that I've seen: actions that are frowned upon are not allowed on the forum, period. It makes no sense to me that the community is giving red trust to people for these actions that are perfectly within the rules of the forum.
Red trust isn't related to the rules of the forum. The trust system is supposed to reflect the feedback of individuals for other individuals. If I find your actions untrustworthy, scammy, whatever, and I leave negative feedback for you, that's my opinion and it's all that it is. As far as I know, the trust system isn't supposed to be governed by any set of rules other than what individuals find positive or negative about their interactions with each other here.