What concerns should I have when buying a "Salvage Vehicle?"?

It is a 2007 BMW 328i with 30000 miles externally it is beautiful. My main concern is of it’s frame. What else should i ask? I NEED a car badly as some of you know a couple days before I got married. A neighbor ran head on into my Mountaineer. Which happened to be parked in the street which i never do and to make matters worse, there was a car parked behind mine. Our insurance co, said it was a total loss. Mind you, the towtruck driver drove it up onto the flatbed truck. What questions should I ask?