Sometimes the customers try it on. It's not quite the same but when I've sold some work onto friends, some customers will say that the price included this and that when it never has.
On another note, I used to help out a mate one day a week on his work. Did so for years. But he had different work ethics to mine and not as particular and so I would do an adequate job the same as he would so we could get the work done. Admittedly we never got any complaints and never lost any work either as the windows were cleaned (trad tools) and the customers were happy. But on my work, I would not have been overly happy. I'm not OCD but I would have kept the frames cleaned on a regular basis did that little bit extra.
So staff might do a great job and not all the customers will be happy (for whatever reasons) and you as a boss might not be happy as its not your standard. But as far as cleaned windows go,,,,, I'm sure they will be clean!
It's partofthe territory of emoloying