I will probably travel to look at the car by the end of january. For what I know (and I have talked with the owner via text and on the phone), the car is well taken care of. No long life maintenance but every year : carbon cleaning then oil change with filters. The gearbox has also seen its oil changed (which is very rare here in Europe). Some O2 sensors have been changed (one was changed last month - 900€ bill), the two front air suspension bags, AC compressor which is an engine out job if memory serves, AC radiator, etc…
The inside of the car looks fabulous.
The only thing not working is the sunroof and the guy told me right away. He never used it so he did not bother having it fixed.
EDIT : But I shall not discuss a future S8 here, no point for me to pollute this interesting thread. Thank you again for the insight.