What is an AMG Performance Center?

I had thought that those would be the centers where you could buy AMGs or have them serviced. There are three dealerships here, two of them AMG Performance Centers. But I went to the one that wasn't and they had the most AMGs. Even a CLS and G. They sold and serviced AMGs. They even had their own AMG mechanic. You know, one of those guys that gets sent to Affalterbach to learn. So what is actually the difference between a regular Mercedes dealership and an AMG Performance Center?