People notice how dirty their windows are when the sun shines on them, hence now is a good time to pick up new work.
Like Wizard I hold out for the price I want, although I do explain that the price includes wiping the frames and washing the sills every time. That usually sells it to them. If they don't like the price, I politely tell them that I will leave it with them if they wish to think about it.
I personally don't find 'competition' a problem. Customers are free to choose their window cleaner and I get on well with most of the other window cleaners I meet.

John.