It is not against any rules to sell your account. If the person sponsoring the sold account still trusts the ratings of that account then there would be no reason to remove them.
If I sell my account, not only does my existing feedback stand, but also any future feedback made by the new owner will appear for everyone, as if the new owner is trusted when he shouldn't be.
I don't see why it wouldn't be against the rules for people to trade accounts. The main reason people do it seems to be to buy and sell trust.