I haven't got much shop work, only a few in Northwood and Pinner (top areas) but what is interesting is that none of them were canvassed by me. In every case they approached me and asked if I would do them. The contact came because my name was passed on to them by a customer or a staff member who is a customer of mine.
Each of them tell roughly the same story, either cant get a window cleaner or fed up with poor workmanship / attitude of existing cleaner.
I charge £10 for a shop and I reckon there is more where that came from but I'm not interested, I am struggling all the time to keep up with what I've got now.