My first time cleans are treated as one off cleans reason being: That's often how they turn out same quote, put yourself in the customers position, if they had minging windows they weren't too particular about having a window cleaner before you came along, so when you've cleaned those mingers, opportunists are bound to cancel so quote new cleans as one offs. The way I look at it is, look at the amount of money they have saved by not having a window cleaner while these windows were accummulating filth.