Purbeast,
I bought a Chevy Malibu LTZ with a 3.6 v6 from Carmax.
I had reservations about going there, but I'm glad I did. There are things that go against them like rental cars and fleet vehicles that I would shy away from.
But that is something as a g37 buyer, you wouldn't have to worry about. 9/10 I bet they are lease returns. I believe that my car is lease return as well.
I ended up getting the extended warranty and I optioned for 125k in coverage. As far as extended warranties go, it's legit. Despite my reservations about these things, I'm glad I got it.
My LY7 motor has a tendency to slip timing chains. My warranty has all timing gear covered. They also directly pay GM dealers to fix it. I only loose my deductible. Which is 300.
They also will fix non-covered parts that is damaged if a covered part causes the failure.
You may want to talk to your friend that works there to get feedback on the warranty.
I think premium vehicles like Infiniti's are a sound buy from Carmax. I wanted an Escape, but those are rent a car favorites.
If you have any questions, reply or PM me.
I hope you get your g37 the way you want it.