Look to see if the previous owner has had any of the following changed during its lifespan
PCV Valve
DV Valve
Cam Follower
If not then its means of haggling the price down by £100 or more if you lie a little. i would also advise that when you do buy it you replace them with the latest revision for your piece of mind. There is plenty of threads about these three things and guides on how to change them. Should cost you around £100 to change all three of these parts providing you fit yourself which is also good learning providing your confident enough to give it a try.
Other things are look at when the cam belt and tensioners have been changed
Also test the air con to make sure it blows out cold air.
Anything else i've missed I'm sure other people will add in
Good luck with buying