Freddy, I take it you've been accused of scratching glass and you've only used your WFP?
If that's the case then why not offer to demonstrate your WFP on a window and try to scratch the glass with the bristles? I bet you can't.
But saying that, if there's scratches on the inside of the window and you didn't do them, then that should be enough evidence.
This happened to a local window cleaner to me, there's no way he could make the scratches (I saw them, they're on a pub) even using a scraper, and in the end he just walked away despite a threat of litigation.
Nothing happened to him, and he - being 100% sure the scratches weren't caused by him - was correct in walking.
And some glass on new builds is rubbish! There's scatches all over it from being brand new; I'm sure the building industry uses the cheapest materials on some of these new houses.