i tend to give em a good clean on the first go, rather do it now than in a few months.
after a first clean i always collect the money that afternoon which gives me a chance to inspect my own work and if it has left dirty drips i simply detail the glass so that the customer is happy.
I always explain that first cleans are a real de- gunging and vents and frames can leave unpredictable results, most custies appreciate what your saying.
and if not.... If you had a tshirt that you wore every day for 3 years without washing and when you put it in the machine it didnt come clean the first time would you think the machine was broken?
or would you just clean it in again?
dont worry sir/madam, i will make these windows sparkle for you.
I DO LOVE MY JOB!!