Simple!
When you knock on a door to find out if they require a window cleaner and they turn round and say, "we have a window cleaner but how much would you charge" Many will try this one to get a cheaper clean. Just walk away. If you were to quote that would be taking customers off them.
There will be pleanty of houses out there who don't have a window cleaner even if there next door nieghbour has one. These are the people you want.
Window cleaning is first come, first serve.
There is a window cleaner who cleans a whole street but one. That is the one I do! They phoned me to ask if I would do the windows not the other chap!
people are entitled to choose who they want.
Never be affraid to work in another window cleaners patch. You are FREE to work where ever you want.
But DO NOT steal anyones customers dilibertly.