- check every single switch on the dash does what its supposed to, esp suspension
- check soft close doors and boot
- check turbo is working properly on drive and look out for black smoke from rear
- check for diesel smells under the bonnet, could be a leaky injector or 6.
- service history as clocking is common play on these.
Don't just take the service book at face value, call the dealers that have stamped give the reg and ask for all services carried out on this vehicle and the mileage at the time. I would be wary if it has been serviced outside the dealer netword by lots of different garages.
Also ensure that no services have been missed or were significantly late.