But what happen if the seller take back his account by proving the ownership of old address after sell the account to someone? Is it still possible right?
Please respond, I'm curious about this one.
No need to worry if the buyer have signed message from the seller when buying accounts, that would serve as proof of account transfer and he cant claim it back
Well when you buy an account you ask the seller to sign a message that that account is sold to you, and you must keep this message for future, so you are protected. - my opinion
its not just your opinion, i agree with it as well. by stating in the signed message that the account will be sold to you, the seller can no longer claim the account back as theirs using a signed message.