How to test for presence of the primer or paint

To make it short, not :help:

I hired a guy to fix some window trim around the house, he recommended another guy - painter to repaint the house.
I bought two 5gal buckets of Behr exterior primer and two 5gal buckets of Behr flat paint, both tinted Navajo White. I think this is my possibly second "mistake", should have tinted the primer a slightly different color so I could see the coverage...
Unfortunately I was unable to see when the work was started, only when it's halfdone.
Looking around the edges of the aluminum trim, I see very little "paint" thickness on the surface. According to the painter he has done two coats, i.e. primer and the paint, but he only started on Friday with one helper and it's a barely 1000 sq ft house, one story though.
Is there some distinctive feature of the primer I can test for? Or can I prove there is either primer or paint on the surface?
I know, I should have been there, but the guy started work on Friday without even telling me he has started :(
I hate to be so paranoid, but I also would hate to have to hunt the guy down if the paint starts peeling off shortly...

Thanks in advance!