To me there are 2 reasons to look at buying a franchise.
First is brand recognition - i.e. McDonalds is known worldwide, everyone knows what McD's food is and what they get. People like to go for something that is familiar they feel it's safer.
The second is a proven system - methods of working, gaining customers, and managing the business etc.
The problem I see with window cleaning franchise is brand recognition - can the public name a window cleaning brand? I doubt it.
So what you are paying for is the management system and a bit of training and hand holding. Unless they are supplying custys.
While it might be a quick route to working and getting custys you will be paying for them as long as you continue being a franchise!