Look for a Porsche that has been serviced regularly by an Official Porsche Centre. This means that the car has been looked after by Porsche trained technicians and serviced with Genuine Porsche Parts.
If you are comparing several vehicles, it may be helpful to put together a checklist of items such as model year, kilometres, performance and features. By going through the same checklist for all vehicles you will get a clearer comparison.
Where possible, buy your pre-owned Porsche from an Official Porsche Centre. This way, you know that the car has been inspected by Porsche trained Technicians and is eligible for a Porsche factory warranty and Porsche Roadside Assistance; both of which can be extended.