depends on how well the car was serviced prio to you purchasing it... when you go look at one do every test imaginable and get service records..

by test i mean blow by checking the turbo if a turbodiesel the differential play the driveshaft slop the driveshaft joints(they arent u-joints) if the fuel tank has a vacuum after a drive look for rust the brakes.. .. so many tests ..especially if your going to want to drive it alot and valve adjustments timing adjustments and stuff...

but hey you can probably have the 750k milage award in no time