Its a 9 year old car so just check everything you would check on any 9 year old car. At that age its a bit of a lottery but buying private and judging the sellers is always a good indicator. If they are the slobs at the wrong end of town expect trouble and run away. If its been owned by the wife of a bank manager who lives in a nice house its likely (not guaranteed) to be better. But still check it over.
As I'd recommend for buying any car, once you have one in your sights, check the MoT history; you can get a very good idea of how a car has been treated and serviced through it's life. And don't skimp on the HPI check!
Even mismatch tires can indicate if it has been taken care of,one good one,try to se the car early in the morning and if possible the first start of the day (cold start).When cold they can bee a bit noisy and you will get a better idea the health of the engine.
If you have access to a fault code reader, or know somewho has one, why not invite them with you?
You may see faults that otherwise are not noticeable, like door handle sensors, HVAC sensors and actuators, exhaust sensors, occasional missfires, short circuits.
Otherwise look under the car as best you can for damage or rust.
Check under the carpets for water/ signs of leakage.
Test every button and feature.