[king marko]

Totally agree with window washer on this one
Just make sure you inform your customers old & new that you offer a guarantee - As long as they contact you within 24hrs or so with any problems they might have regarding the window clean, then you'll happily return and rectify

I offer this and can honestly say I've never had a call back  

Being polite, courteous and getting to know your customers works wonders too  

[H2GoKent]

My favs are the ones who say its about to rain.
I sometimes smile sweetly and say. 'this is England it's always about to rain, that's the peril of living in the temperate zone'
Some laugh, some smile some think I'm mental. But no one argues usually.

Fact is if you want to make a regular living and they want a regular service then you almost have to work in the rain. you have to train your customers up.