I think a formal mechanism for selling accounts would be better than a backdoor mechanism. For example, scammers might want to buy accounts with a strong reputation to help push the scam. If the account were sold through a formal mechanism, the system could reset the reputation while those sold on the open market would not reset the reputation.
BTW: Selling accounts involves the IP rights related with an account. In some cases the seller might want to sell IP for images and texts in the account. In other cases, they might want to retain the copyrights. Such things could be stipulated in a formal contract and recorded on the blockchain.