Did one a few weeks ago one off job, one egg + one pane of glass = £35 
Could work for free, but that would be stupid :
Yes, I can just imagine how that went.
Custy "I've got egg on my window, can you clean it please?"
WC "Yes, I'm only 5 minutes away, I'll be there in a moment"
Custy "Oh good"
WC cleans 1 plate glass window in 10 mins, "35 quid please"
Custy "That's fantastic, thank you for taking 24.75 minutes from your busy day, would you come back and clean that window again if there is any bird poo etc on it?"
WC "Yes Ma'am, just doing my job" (Mission impossible theme plays in the background as WC zooms off in his batmobile)
I think someone here works in Sainsbury's filling shelves and pretending to be a window cleaner. If this person had a fatal accident and an autopsy was performed, the pathologist would remove the top of his skull and find a 1/4 pound of boiled rice.