Yeh mate those are the 18" winter wheels, or standard rims, they really dont suit the car.
That car made 18,900 last time it was on, which to be honest is a fair price considering the mileage of 80k
The RS6 is a car that I bought very very carefully, it took about a month of research before I actually went looking armed with all the info you need to know.
There is no doubt that the safest place to buy is from a Audi dealership.
However if your very careful and you know what your doing and you dont need finace etc, then going private could well get you a better example.
I dont like that guys advert, I dont like any advert that isnt upfront amount some info, like amount of owners, the history of the car etc.
Im pretty sure he wont sell it on there, unless he is prepped to take 19k for it, as the car most likley needs 3-4k spent on it, for starters it needs proper wheels, it most likley needs a cam belt and service, and to top it off its bound to need brakes !! there you go.