I dealt with this issue recently, and the answer varies from state to state. For mechanical issues, aftermarket parts aren't the worst things in the world, as they often have worked out kinks that OEM parts may suffer from. They also drive down the price of OEM parts, simply by being available. For cosmetic issues, there is no reason they can't use reconditioned parts at a minimum. Who was at fault? Who's insurance is being used? If your insurance covers OEM and theirs doesn't, file with your own insurance and let them go after the driver. If you're using your insurance, than go to the body shop and see if they can get their parts supplier to match aftermarket pricing on OEM parts. In many places, you don't have a dog in the fight. Your best ally is the body shop itself, as well as your own insurance provider. When I wrecked my truck on ice last Feb., I ended up with many reconditioned body panels. Considering they were sanded, painted and reconditioned, but OEM, that didn't bother me. I had to settle for an AM radiator. From the issues supposedly associated with the OE radiator, that may not be a bad thing? Best of luck.