Some great advice above, just to add the prep on the car is terrible imo, I'd be embarrassed to show those photos, also the fact the owner was a Dr means little if anything imo.
The parking sensors look a bit tired and worse for wear, I'd guess there may be other bits the same like the wheels could do with a refurb, all leverage for negotiation.
Do you know the registration so you can check the MOT history?
If you do go ahead I'd personally ask for a fresh MOT at a local garage of your choice (not one they suggest/use)
How does it compare with similar spec/mileage Q7's?
Good luck with it in any case.