Hmm, have you seen any precedent to this?
Do the admins support someone who can prove that they have bought the account over someone who can prove that they originally owned the account?
I know that they are okay with account transfers, but I don't know to what extent they enforce account transfers.
Do you have any experience with admins stepping in and helping an account buyer over the original account owner?

I think that the account was hacked, though this can never be known for certain.

The IP that posted the loan request from yussuf89's account also posted this:
https://bitcointalk.org/index.php?topic=960603.0
Someone with the same IP was trying to sell another account here, presumably hacked:
https://bitcointalk.org/index.php?topic=925024.0

yussuf89's password wasn't changed/reset recently except for when marcotheminer did it, so the attacker must have somehow gotten his password. Keylogger or phishing, maybe.

Zeki's IP matches yussuf89.

Since ownership of the account is contested, I'm thinking that I should not restore the account and let people give trust ratings depending on what happens. For example, if marcotheminer needs to eat the entire cost of this when he's mostly not at fault, some people might want to give yussuf89 negative feedback.