Banned - failed to resolve - https://www.epicnpc.com/threads/894043-Account-recalled-by-SpartanMD/page2
Make sure he has rep, if he is new to MD, he could have previously traded with that account and might know the sq/a to change password/email.
He can also delete everything on your account, including the characters, but that all can be reverted (although it can take weeks to be done).
I highly suggest you make sure hes repped before anything. You can try making him give you collateral until hes done. Also, add an authenticator, really helps as he can't do much even if he changes information.
But to your general question, no, he can't "hack" your account, he can only screw with it.
