A body shop with the same name as your GM dealer buys parts and paint from the same place others do, usually mandated by the insurance estimate. If they can get the same class of part (OE, OEM, LKQ, used, rebuilt, after-market, etc) cheaper than the source cited in the estimate they do. They do not get any discount by buying from the dealership they are associated with. They are usually an entirely different entity.

Don't think that if you buy a used car from a dealership that they will use the dealership service department for used car warranty work! They use cheaper shops and parts.

There is absolutely NO reason to use a Dealership body shop except that you want to. They do the same job for the same price using the same parts as the guy down the street.

Use anybody you want, don't think a shop associated with a GM dealer has anything special going for it.

I guess I am ranting, I keep hearing things like "I don't want to buy a new car out of town, and save a couple thousand dollars, because I would have to go to that dealership for warranty work". B.S.!!!

The Service Department and the Parts Department and Body Shop may be owned by the same person/corp/LLC but they are different entities that choose their own suppliers and their own profit margins.

The absolute worst Body repair experience I have had is at a Toyota Dealer body shop on a Toyota Pick up. They did everything poorly and took 8 weeks for simple fender and bumper replacement. They really sucked!
The second worst was at the Chevy dealer body shop on my 2008 HHR. They did not even know the people in the parts department next door.

I will put the soapbox away now. Return to your regular activities.