I've knocked a fellow windy's door canvassing before. Awkward but we laughed it off with a 'if you're too tired when you get in give me a ring' type of thing.
I've never had much in the way of 'turf wars' that you sometimes hear about as I always had the mindset of never stepping on another window cleaners toes and when I'm asked for a price I always ask do you have a window cleaner before giving a quote and politely declining if they do.
You'll be amazed at how many people are still out there who need one but don't, new people moving into the area, younger people who after spending their money on nights out, kids etc settling down and signing up to a service to keep the house in order like windows, gardening.
The people to avoid like the plague are the ones who tell you they had a window cleaner who mysteriously disappeared, 9 times out of 10 they're complete messers.
All part of the fun James, just remember to keep at it and don't give up as it'll take a good few years to get a round to where you want it to be, even then you'll need to replace customers moving away or older folks going into homes or deaths.