let me give you some advice
go and do your windows, and do them how you would normally clean a customers
don't touch the top frame, scrub do your w thing up and down the window, take the brush of rinse properly if it doesn't sheet you know you have to run the jets all the way down and across the window, when it comes to patio doors just spend more time rinsing,
have a look at the results, remember you might not get 100 even trad leaves some marks during the course of the day, just got too make sure its not too many
once you've done it right you will be fine just clean the windows, that's all there is to it,
if they sense you are doubtful do you think they will be enthused by your lack of confidence?