[richard groves]

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&ved=0ahUKEwjs0pbW5a_XAhWS6KQKHfuTCuAQjhwIBQ&url=http%3A%2F%2Fwww.lakestatecleaning.com%2Fwhy-does-glass-scratch%2F&psig=AOvVaw0TM3HsJj06xi3zvxNfbEcG&ust=1510258551606906

[paul alan]

Sounds like they are just giving potential customer's a reason to use their service.

Besides even if a window cleaner is aware of fabrication debris it wouldn't make any difference as its not visible to the eye.

Even if there is some type of equipment you can use to identify the problem it wouldn't be practical to use.

[nathankaye]

Cheers Barry but I also agree with Paul Alan. Lol I thought I can waffle to make a sale. It does make for an interesting read but I must be one of the uneducated window cleaners they refer to because if I look at the pane of glass the same as this company, I wouldnt be able to tell if it had invisible fabrication debris on it. 

[richard groves]

Maybe.
My point was though that IF there is any truth in that then it is entirely plausible for fabrication debris or other debris ( e.g. cement and builders dust  ) to be dragged across the surface of glass and causing a scratch 

[richard groves]

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjwpuyT86_XAhVSIOwKHcVACfgQFggoMAE&url=https%3A%2F%2Fsimple.wikipedia.org%2Fwiki%2FMohs_scale_of_mineral_hardness&usg=AOvVaw3_ceaoie4ZU2qNYselAQkw
 
The most common constituent of sand is quartz.
Quartz is harder on the Mohs scale than glass.
even the tough gorilla glass used on smartphone screens are prone to scratches from sand.
Just saying

[nathankaye]

Maybe.
My point was though that IF there is any truth in that then it is entirely plausible for fabrication debris or other debris ( e.g. cement and builders dust  ) to be dragged across the surface of glass and causing a scratch 

Sorry bud!! On same page now. Cheers

[richard groves]

I've had a very similar experience myself several years ago.
Cleaned brand new tempered glass doors after a building extension had been completed. Lots of dust etc.
Needless to say, I denied all blame. blocked number and never returned .
It was a lesson learnt though and I have been extremely careful in such situations ever since.