Accident damage
Look at the car from every angle. If the doors and wings don’t match up, the car has almost certainly been in an accident and not been repaired well. Look for irregularities in the paintwork, too, such as subtle changes in paint colour, ‘runs’ or ripples, or ‘overspray' on window rubbers and inside wheel arches. Check suspect areas with a magnet to see if filler has been used to repair rusty areas. When driving the car, the steering should be straight with no tendency to pull to the left or right.
How much use has the car had?
Check the speedometer mileage. Does the mileage correspond with the general condition of the car? Look for wear on the brake pedal rubbers and gear lever, a shiny steering wheel or sagging seats as a tell-tale sign of high mileage.
If the condition is good and the car has unusually low mileage, check that it hasn’t sat unused for long periods or only been used for short journeys. Both can cause problems. Also if you buy from a used car dealer, if the brake discs are rusted-up or if the car has a 'flat' battery, it's probably been standing there for six months.
Under the bonnet
A very dirty engine area may suggest that the car hasn’t been looked after and that servicing has been neglected. Equally, a sparkling clean engine could have been steam-cleaned to disguise problems.
Check the oil level and colour of the oil before you start the engine. If it’s low or dirty, check when it was last changed with the service schedule to ensure the car hasn’t been neglected.
If you find grey sludge on the dipstick, the oil filler cap or the oil breather pipe, walk away and do not buy.
The coolant should be the colour of anti-freeze, not rust-coloured. An engine that has been run without anti-freeze may have problems.
Check no oil is leaking from the engine, gearbox or suspension.
When you start the engine, the oil light should go out soon after it starts. There shouldn’t be any rattles or knocking noises, even from cold. Do remember though diesel engines are usually noisier than petrol.
Watch for signs of overheating on the temperature gauges.
Transmission
The clutch should operate smoothly and all the gears should engage easily.
Check for clutch slip by driving the car up a hill in a high gear.
On the test drive, change down into each gear from a higher speed than normal to test the synchromesh. If the gears crunch, or if the gearbox whines, the car may need a new gearbox.
Tyres
Check the treads and sidewalls on all tyres – including the spare. Anything less than 1.6mm of tread is illegal in the UK, but ideally each should have much more than this. The sidewalls should have no signs of damage or any bulges. Uneven wear suggests steering, tracking or suspension problems.
Suspension
Push down at the corners and let go. The car should rebound once just past the level position then go back to normal if the shock absorbers are working.
If the suspension knocks on bumpy roads or the handling feels imprecise, it indicates worn bushes, a broken spring, worn joints or shock absorbers.
Steering
Turn the steering wheel gently while a friend watches the front wheels – there shouldn’t be any delay in the turn and the wheels moving. There shouldn’t be any free play – and the car will fail an MoT if there is.
Unbalanced wheels lead to a wobbly steering wheel at higher speed, if this happens wheel balancing is usually available at your local tyre & exhaust company. Never ignore wobbly steering even at lower speeds, it could mean your wheel is about to drop-off.
Brakes
The brake pedal should feel solid and never sink to the floor before working.
A car should never veer when the brakes are applied hard – even suddenly from high speed.
A car juddering or wobbling under braking is probably suffering from distorted front brake discs.
Check the brake hoses under the wheel arches for swelling or leaks.
Finally, don't let something you love about the car, such as the colour or the music system, cloud your judgement when buying, remember a great stereo is no good if the car falls to pieces next day.
Good Luck