If a new customer asks me to clean their windows I weigh up if they are just wanting a one off for end of tenancy clean and bye bye. If they have lived there for years, house is in a right state and they plan on selling. Do not want to take on extremely hard, new, first and last cleans which will take at least twice as long for twice the price, twice the time and twice the effort. If it's a genuine ideal customer who has just bought the property that's a different story, don't mind doing them.