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You missed the point completely. IF trading accounts is not allowed in forum policy, then buyers would know that sellers can take back the account at will, and that will drastically reduce trading and hacking.
In this particular case bayuo can't get back his original account as Theymos is not sure if it was indeed sold or not. If policy was that trading is not allowed then the decision would have been easy.
Theymos didn't recover because he didn't get enough evidence. Why there is no such policy is because we can't know whether it is traded or not. Seller can always come with a new account and sign from his BTC address and tell I was using it. It will always became a problem. Theymos told that if he didn't get enough proof on the first message he avoid users future message too. So he might have avoided bayou. The better thing to do here is to freeze the account. Giving back to real zedicus, he might sell the account to another person.
~~MZ~~
Badbear and hillarious are saying its because there is a chance that he might have sold it. If it was not according to rules then he would have got it back regardless of whether he sold or not. At least it would have been disabled.