The other thing is it is an insurance risk for them. That'* why customers are not usually allowed around the vehicles.
In the two instances you are allowed backk there and around are a place you used to work, and your brother'* shop. I would assume your brother would be taking responisbility for you (whether stated or not) and at the one where you used to work, they probably assume you know the deal from working there.
The other thing is that if you are taking pictures, the flash can bother the mechanic, getting in to get a good picture will bother them, and they don't want to have to wait til you get the picture to continue.
I'd say if you want it documented, then either do it yourself, or visit one of the above two places.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4