Whats should the Tire wear be on the stock 17" tires?

What are the stock tires brand/size?

I am looking at a 03 350Z Coupe Enthusiast 6-speed that has 12k miles on it and the rear tires are much more worn than the front.I am going to get a Nissan service dept to give the car a good look over to see if the previous owner abused it too much.

Thanks for any help on the matter.
Dane