Why do I have to pay a deposit?

Two days ago a mother of a bride called me to cancel, two months before her daughters wedding. I had already turned down two large weddings because I was booked. When she called I went scampering off to see if the other couples had already booked other photographers which they had. Now although I have promised the cancelling bride that if I manage to sell the date she would not loose her deposit. But it’s unlikely that I sell the date at this late stage. So the thirty percent deposit helps cover the loss of earnings incurred. I am sorry for the bride who is cancelling because she had a change of heart, but I am running a business. I have a booking manager because I am a big softie when it comes to the hard stuff. A big softie who was making no money till I hired my precious booking manager.