God alive, as it was said above the easiest thing is for them to compare to another car! It's not rocket science. Sadly these things are only as good as the person doing the job and their knowlege and skill.
This reminds me of when I had a Golf and they did some work at VW main dealer Bodyshop. I was telling them
how to paint the darn thing, on top of that they couldn't get the position right with the badges on the tailgate (it had a new one) I was out in the car park showing them as they were saying there is no factory spec or dimentions given to work to. As I turn around and counted about 15 other Golfs in the car part around us!!!!
Then I handed them a print out of the dimentions which should be in their body repair manual from an online source, and they were more worried about copyright of where I found it online. They lost a customer from that point onwards.