This case can be complicated and in the past, there was discusion on account sellers are ready to sell their Bitcoin wallet / private key so that the account buyers can sign Bitcoin messages too.
I think what is needed is for the accused to sign a message. If they are able to sign a message, it doesn't matter if the account seller sold their bitcoin wallet also. This forum is not FBI, who is actually going to investigate all these? It will just end us in assumption.
If the whole situation still looks suspicious, shasan should refuse the loan request and blacklist the user.
But if a user is able to sign a valid message from the right address, we should not down play it because that is the most reliable working tool we have in the forum.