C'mon James, you should know this by now.
The longevity of the turbo depends on the following...
- How hard was the car driven?
- Was the car cooled down properly?
- How often was the oil changed? Does the PO have any service records to backup his claim?
- Has the car been modded? If so, has the boost pressure ever been turned up above stock?
If it were me, unless the PO has a lot of the service records, I would stay away from a newer Audi that has high mileage. As you know, my dad has an '09 S4 and it seems to be in the dealership more than his driveway. Even though it's small stuff that fails, it adds up and gets old after a while.