If they've wasted my time before & try to book again, I gave them time, date, location when they last wasted my time & tell them that I want 50e phone credit off them before I accept any further business. I've only ever had 1 previous timewaster buy a credit, the rest have not bothered. My work ethos is once a timewaster, always a timewaster unless they're prepared to confirm their appointment with phone credit.
Sandy x