yes i do, all the time, it does make a diffrence, when the window is left open! erm price, well i've have been to cheep for to long so thats a bad start, but it all depends on how long it may take you, how clean they want it ie a wipe over or the sparkle, say at least the price of the window, as in what you charge to clean for a normal wash, if not twice the price, you will live and learn by it.