Dai
Thats a difficult one then?
Is it worth going around your cleaning areas and ask them yourself, you can normaly tell if the places have a window cleaner, or just pop into the reception, and ask there, the only other way is to ask this guy, were they are and you will think about it, But i really wouldn't want to hand money over if its a continuose payment plan, like i said if it wasnt to much for a one off it might be worth it.