Confidence, that is the key. You are the boss, you know about window cleaning, not them. You tell them its a myth that you cant clean in the rain, make them look silly, tell them that all your other customers love the fact that you'r service is all year round, DO NOT BACK DOWN. Pre warn customers with bad frames that the finish might not be much good. Yesterday I refused a job and told the man I would only clean the windows if they were re painted. STAND YOUR GROUND and DO NOT be embaressed about charging a high price.
How to close a deal:
give all your selling points ( frames, insured, safety cones etc etc )
number of windows, the customer will be suprised!
then state your price and close your mouth, let them say the next word.
Trust me this will work, Luke