As I understand it, accounts trades are frowned upon but not explicitly forbidden because it would be nearly impossible to enforce whatever consequences efficiently.
Even if they were banned, they wouldn't stop; they would simply move off forum.
I would be most in favor of changing the rules regarding account trading to be in line with scams. That is to say, remove the line in the "Unofficial rules" saying they are allowed, but replace it with a line saying they are not moderated. Buying an account is buying a reputation/rank/trust which you did not earn. That is inherently untrustworthy in my opinion, and generally speaking I would be against removing negative tags from these users.