Welcome Paul to the forum, be nice to see more of ya round here!

Window cleaning patch, lol. Go for it mate, when i started (and the same now, just not so often), i took loads of customers off other window cleaners. But only because they were not regular, or did rubbish job. I never knowingly undercut other cleaners, on principle. If i know how much they charged, i aim for the same or preferrably more. On occasion i have unwittingly gone cheaper, but ive always made a point when asked to quote to make it clear that I dont undercut their previous window cleaner, but I am always happy to take over if they are not happy with the service he/she offers.
No such thing as patch, so long as you arent consistently going in stupidly cheap, nobody else should have a problem. Try to make sure you are getting the pricing right, otherwise you will only be shooting yourself in the foot. And good luck geezer!

My view is if i am doing a good job, the customer will stick with ya. and if they are that cheap that go to the first person that undercuts you, good riddance. When they come back, or if they come back because he drops out/puts prices up, they will pay more for the privledge if they want me to do them again!