Sean
I live in the south of birmingham and I have work very close to you, my charges are £12 minimum and I charge more for 1st cleans, charging £7 is silly and £5 downright stupid.
Quote high, and if they say wow, sell yourself and your services to them, expalin what you do and why you are the best.
Forget the comment on council estates, I have loads of customers who live on council and not every tenant is on the dole and broke.
Also tell your customers that it can take 3 cleans to get the windows in a perfect condition but if they are not happy with the clean to call you and you will be back straightaway to sort out.