Funny, I had the exact opposite experience. For OSH Stencils, they had a scaling issue with their setup that I pointed out to them, and they just shrugged and said that was the nature of the beast essentially and they couldn't do anything about it. They might have said something about Kapton shrinkage or some such. (I don't currently have the exact numbers, but it was off a couple of percent linearly, which doesn't matter for a tiny board, but for a 4" board, the difference adds up, so that if you align the apertures on one end of the board, they don't on the other side of the board. Like the aperture was off by a whole 0603 pad or more). I went back to Pololu for that same board, and everything was spot on. And I have had zero complaints with them since. If I had to complain about something, I might slightly ding them slightly on the super-tiny aperture shapes and the kerf width of their laser. But everything has always worked. Apparently YMMV.