This person is doing the classical cashier check fraud with a deposit on an apartment. Sending a cashier's check with a few thousands extra money, to be spent on the flight for his supposed daughter. When you fall for this trick you will try to cash the check, pay the cronies of this person, and then find out that the cashier's check is a fake and bounces a few weeks later. At that point you have lost your own money..
Don't fall for cashier's checks that are of a higher amount than what you are charging.