First thing to check is steering: while the car is in situ, turn from full lock to full lock, if there is any creaking/noises, it'll need some work done there, possibly to steering rack
Usual checks for smoke etc if it has high miles, also check what it's like on a cold start, chances are it'll be a bit spluttery, but to be honest, it's a common fault.
If you are looking to buy one at that price, you'll be looking at about £400 - £700 for the dpf removal and remap (this will also include an EGR delete)
Mine is just about to hit 100k and everything is going fine, a few niggles but none I can't sort myself, have to clean inlet manifold.
Make sure the water pump and belt (the name is eluding me) have been changed at approx 70k (?)
There are more, but it is too early in the morning for me to think of them!