I have had a few lads say things like this to me, in the hope I bend to their request to stay away from their "patch". But, I know it is not their patch at all, I know that there are several window cleaners in their so called patch. I know it won't make the blindest bit of difference what agreement I come to with that individual, because someone else will approach my customers sooner or later. But I also know that sooner or later I will approach theirs too.. not because they came on to my patch, but because they do not care and I do not care. And the reason neither of us care, because we both know it makes no difference.
You are not likely to be your customers first window cleaner, but you might be their best one. The difference between a good window cleaner and a bad one is huge for the customer, because the mistakes build up over time. Eventually they look really bad. If your customer leaves you, it is because they expect the same job done but for less money. If a customer leaves them, it is because they want a better job for more money.