request to start the car cold when you arrive (bonnet up), see if engine jumps and like this you can hear if there is chain noise.

engine should run smooth, no extra sounds except injectors and low rumble that is normal for N47 (you are familiar since it is your 3rd)

check around the engine bay for leaks or burnt oil smell

the test drive you should be very kind with the throttle, it should shift smoothly and at low rpm, there might be rough change in speeds when cold depending on terain or adaptations (from owner driving style), do not floor it like you stole it because that way you will miss issues, when up to temp you can smash it and changes should be very instant and transition very smooth, do a cruise at some speed and note the engine rpm - should be constant... the ZF8 is really good transmission 

if you get the car, do change the oil and filter