depends on several things. if your buying from dealer. garage. check the car has been serviced regular, at correct intervals. check if the car has cambelt? has it been changed correct interval. is there proof of it by receipt or stamped into service book,
have a look under bonnet, check oil level, water level. see how clean the oil is, is it creamy? possible signs of water in oil ( bad signs).
start the car and see if water is bubbling.( bad sign too) check all the tyres have good tread left on them., take car for drive if doesnt steer straight then something wrong too. , even check round door seals to see if car has had panel damage, obvious signs are that there is some welding. and they havent put cloth or trims back properly?!, if you suspect the car has major faults in any way leave it straight away. you can haggle over the price if your happy with it.
ive never owned a new car, so have done this with every car ive brought., btw if you buy from garage forecourt they should give you 3 months warranty just incase you take the car get 2 miles down the road and it goes bang! if they wont offer this take into consideration how much something may cost on the car, and haggle.
been down this road too many times