After much thought, I pulled away from doing this. customer threatened to report me to the Trading standards.
I explained the situation to them calmly without getting angry or heavy with them and they just got abusive and threatening.
If I was not busy I would go after it but as I am I just explained why I could charge them and then pulled back.
The Law is that if you can get proof that a booking is real and the customer cancels without reason within an unexceptable time then you can Charge.
Dentists do this as do some doctors, and you never sign a contract with them.
I do see the point about walking away though and the effect it could have on future business, its just that I dont do it.
Customers want it both ways, they want you on their own terms and its something we have to live with unfortuantley.
Cheers
Neil