No matter what anyone says or thinks of these charges it can also work for people, I knew of a lad who charged £2 and £3 for front only. he had a good few streets of these terraced houses, a window upstairs and one downstairs and then a front door, he only did fronts, park his van up and could do 30 house fronts in a street in just over an hour no problem, he would have a few roads of these houses and clean up no problem, he was also that cheap no one took his work.
If he lost a house or 5 houses for that matter then it didn't make much difference. you lose a £40 house that takes an hour then it makes a hit on your days money.