Rental and deposit refund if cancellation

I have a problem with a future tenant wants to rent my property in Knokke, appeared on your site for a week from August 18 to 25, the latter does not want me to pay the balance after entering the apartment. What has not been agreed at the outset, the more I use my approach to all tenant and for all rental periods: ie you pay prior to arrival on site and take possession of places. After various proposals made to it (site prior meeting ...) this person is talking to me about his positions even scam because I want to join what she needed. I want to know whether or not I should repay the deposit paid or since we decided not to go further in the rent, the deposit is lost?

Mrs. C., from Knokke

contract (even oral) must be performed as specified. If it is intended a deposit and pay the rent in advance, there is no reason to depart from what is contractually agreed. It should not only not make the deposit but also require, if necessary by mail, the payment of rent. Especially not give the keys without payment.