Corners of the new windows are very dirty or scratched

No, then it would look different.

Apparently, you lack the necessary imagination for a possible cause of damage. And of course, there is a defect here. An item is free of defects if it has a condition that is usual for items of the same kind and that the buyer can expect based on the type of item. Such windows, or their condition, are not usual and the builder can expect a better condition. It is possible that a rework could lead to a defect-free item, but that would still have to be proven...

You are right, I am not fantasizing, unlike others here. Let's wait and see what the window fitter of the OP has to say.

the corners look really awful, but they can still be reworked. however, the chamfer will always end up quite large. not exactly a visual highlight. probably nobody will replace it. if you have individual awarding, of course you can't pay the invoice. he can just uninstall the stuff again if he wants to get his property back. of course, be extremely careful that he doesn't damage anything else and if he does, bring out the big hammer right away... (legally not entirely clean ^^)

here's a picture of what a proper window edge looks like. imagine the dirt is gone, the window cleaner has already been commissioned...

our windows were assembled on site. meaning the profiles were cut and glued. only the glass arrived beforehand. such damage to the profile cannot occur during transport....

and what came out ??

Hello,

I was away on business until yesterday evening, so there’s nothing new yet. The window installer basically answered my email: "Everything is normal, it just needs to be cleaned."

But I have already arranged for an on-site inspection to take place first. Either today or tomorrow, I will report back.

So, we have now agreed. I will (try) to sand down and clean the corners as best as possible. As a good will, we will get a discount on the window sills inside from the window fitter.