No Thanks wrote:
I've just had a double glazed door fitted.
It has a couple of finger prints and what looks like a bit of mastic
stuck on the inside between the 2 sheets of glass.
I probably wouldn't have noticed them if I wasn't cleaning the glass
and removing all the wee bits of cut upvc.

I thought the chances of this happening were slim as they would be
made up in some controlled area, or is that just wishful thinking?

Would it be reasonable to complain about this as it isn't noticeable
until you look closer?

it's a defect. the manufacturer is obliged to replace the sealed unit to
your satisfaction. if they don't like it they ought to ensure proper QC.