However if account sellers and buyers deal well, it's not big problem for account sellers to give buyers all necessary information of sold accounts: from email address, email password, account information and password as well as 2FA activation code. So if they did everything well, they won't have to use forgotten-password function and no need of removing 2FA.
The high chance of this being possible is if the deal (selling and buying of the account) was done physically and both parties knows themselves but if it was not a one on one deal and was an online deal without both parties knowing themselves, there would be a limit of how they can trust themselves, so I doubt if all information about the bought account will be completely handed over to the buyer and even if the buyer gets all the information from the seller, they may fear that the seller can collect back the account from them and they would want to change the account information such as password or the email.
Assuming it's a one on one deal and all account information was handed to the buyer, the buyer can not have the same pattern of writing with the seller or the account owner, that's still a loophole which it can be detected that account have changed hands.