If you cancel the contract then you need to feed their mouth with your money again.

Suppose you have paid them 6000QR as down payment, next day if you cameback to them and want to cancel, then you have to add them more money 1200QR to complete the 7200QR (40% of 18000QR), by then you contract will be cancelled. And you get zero riyals returned.

I could not imagine how stupid of myself can be trapped that easy by them.