i hav charged custys for not cancelling jobs before, a booking over the phone for your services is a legal contract, therefore if u hav booked in a mornings work for say 100 pounds then if 90 pounds of that was your labour charges and petrol expences you are within your rights to charge them this amount for loss of earnings as u hav no way of filling these 3 or 4 hours as your work is booked inadvance and they not u hav broken thier verbal contract
a firm i used to know ,not trading anymore but was all over the country, used to charge custy the cost of job if they turned up and thought it was uncleanable
in there opion the custy shoudnt hav wasted thier time making a booking for something what wanted throwing in the skip