This thread is a bit old, but all the info in it is still useful - Buying a Used V Checklist.
One potentially big thing that I don't think is addressed in that thread is front frame rail rust. See here - Warning: 2007 CTS-V Underbody Rust on Front....
One potentially big thing that I don't think is addressed in that thread is front frame rail rust. See here - Warning: 2007 CTS-V Underbody Rust on Front....