After having a series of observations, I discovered that there are no formal rules governing the buying or selling of Forum accounts. Despite how large the forum is, there are supposed to be some rules that must be adhered to when accounts are sold or transferred.
I discovered this thread 
account change hand, and checking the trust feedback of the affected account  trust feedback.
I realize that if there are standard rules governing the transfer of account and the victim complies with the forum's standards for account selling or changing ownership, there won't be any problems with such trust feedback.
By the way, I don't see any reason why account selling or transfer of account should be allowed in the first place. It's not that difficult to create a forum account so why should account selling be allowed? But Since the forum already permits account selling, who am I to challenge it?
You cannot allow and discourage something at the same time. This is a contradiction. I believe that particular rule should be reviewed; either selling accounts should be completely prohibited or allow for the avoidance of future issues like this.

What is the way forward?
In my opinion, the following methods and procedures should be followed when changing account ownership.

- Formal announcement should be made prior to change of account details such as email and password with a signed message

- All deals should be completed with prove if possible

- Accounts from hero to legendary rank should not be allowed to change email in order not to be able to sell such accounts.

- Accounts not active for a year should be temporarily disabled and can only be activated after passing some verification that seems suitable by the administrators.

- Change of account email should have limit to avoid multiple change of ownership within a short time.

I believe that the above will, in some way, help to reduce the scams associated with account changes and to also discourage account selling.