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.
There seems to be very few "hard" rules here. Many of the things that are impossible to enforce (like account selling)
aren't outright banned for that very reason. If someone trustworthy like you were to publicly sell their account,
it would be at the minimum removed from DT and receive neutral feedback that its sold and probably a few
people would neg it too.
I would leave neutral feedback saying the account was sold on whatever date.