On Mon, 4 Dec 2017 14:13:10 -0800 (PST)
Peter Smithson wrote:

I have a long plank of wood I could use. But even if I show that the
frame is bent, they'll say it's the bricks that the frame is mounted
on which doesn't sound right.

If they do you just have to point out that the fitter should have used
packing pieces to compensate for the unevenness.