Account trading should be banned. If I see a Hero or Legendary member posting I assume it has some weight. It won't be if I am thinking this may have been some scammer buying accounts.
Don't assume that then. Even if account selling was banned it would still go on but behind the scenes and just push the business of doing it even further underground, and it's for this reason that it's allowed so people know it goes on and can be weary. Don't just blindly trust people because they are a certain rank or have a little bit of feedback.