Usually if you buy from some auction's you get 1hr to drive the car to confirm it is as described with no hidden faults etc before you pay. Once you pay then its game over & your stuck. Whats you price range? Ex lease cars may well be approaching mileage that involves dpf replacement and I doubt if any would of had there gearbox serviced @ 75K as dealers still don't recognise this as a service requirement. Pressure converters are an issue on high mileage cars as well as both thermostats failing (not obvious due to no temp gauge), failing vac hoses, failing glow plugs & there controller & dpf regeneration problems. Some of these issues lead to EGR and throttle body problems. All can be fixed if you know how & have the cash BUT guess work on these cars usually turns out to be a very expensive hobby!