Outside Checks
When walking around a car, focus on the following:

1. Panel gaps; it should align with the rest of the car. Worry if a front wing is closer to the bonnet at some point. Poor panel fit nearly always gives shoddy repair work away.
2. Body fillers; check for body fillers all around the car, it usually indicates a recent or past accident repair. Filler is almost always visible; crouch down at the front or back and look along the panels.
3. Uneven paint; Look for signs that indicate the paint on one side of the car is different to another, it usually means that the part of the car has been re-sprayed and it might be due to an accident - not all repairers can paint to factory standard. Also look along window rubbers and other trims for signs of overspray.
4. 'Bow legs'; crouch down again - does the car sit straight? Are the wheels aligned correctly, or are they at funny angles? Are the wheel gaps the same between the arches of each side? No to any of the above indicates chassis damage.
5. Worn tyres; is the tyre wear even? If not the alignment may be out. Be careful to inspect the insides of the tyre to check for uneven wear.
   

Inside Checks
Open the door; any theft damage around the lock or handle? And, once inside, check for:

1. Shiny plastics; mirror-like steering wheel, gear knob and pedal rubbers suggest 120,000 miles, not the 20,000 miles on the clock.
2. Soft worn seats; A well worn or saggy driver's seat suggests heavy usage. Look at the driver, check the mileage, is the wear what you'd expect for the two?
3. Seatbelts; do they return properly, are they worn or broken. Be very wary of any damage to seatbelts.
4. Under the carpets; lift the carpets in the boot, to check for crash damage, rippling or any welding marks. Also check the VIN (Vehicle Identification Number) with the one on the registration document, do they tally? Damp carpets in a convertible suggest an ill-fitting hood, or a careless owner, ask why they're wet.
5. Odometer alignment; the numbers are not normally uneven in the display, so if they look uneven it could be because they have been tampered with.
6. Theft damage; Is the steering column damaged? Are there glass fragments under the seat? Does the door trim not fit correctly? Joy-riders don't care how much damage they do - either visible or under the skin.
   

Under the bonnet
Okay, so you're not a mechanic, but a few simple checks can reveal a number of critical and expensive problems.

1. Temperature gauges should be in the normal zone after a short drive - worry if they're not.
2. Look under the bonnet for leaks of oil, water or hydraulic fluid - watch out for smoke too.
3. Check the oil filler cap for white residue or foam. If present, the cylinder head gasket may be faulty.
4. Check the oil level; if it's low or sludgy then the owner is unlikely to have changed it for a while.
   

Documents

1. It is important that you get as much documentation with your car as possible. The vital documents are the Car registration and ownership document, it should have the seller’s name and address on it. You can cross check this with a reasonable form of identification the seller should provide to you.
2. The more documents you get the better. Past MOT certificates and receipts for repairs and parts give a good idea of how well the car was taken care of.
3. Check the registration number, colour and the VIN and engine numbers tally with the car.
4. Make a note of the previous keeper's details - you can contact them to confirm details of the car, such as mileage, condition and any damage details.
5. Make sure you see the original document. If the seller can only provide a copy, be suspicious.
   

The Test Drive
When you test drive the car, ensure that you are alert to any unfamiliar sound form the engine and the rest of the car including the tyres. Do not speed or have the radio on too loud, if you can do not switch on the radio during the test drive.

Start-up
the first few moments in a potential car are often the most revealing. You have no prior knowledge of any problems to 'drive around', and cold cars are more willing to display their faults than warm ones. Therefore, immediate doubts should be raised with 'pre-warmed' cars.

1. Oil pressure light should extinguish almost immediately upon start-up. Suspect serious engine wear if it doesn't, or appears again during the test drive.
2. Smoke shouldn't be apparent, especially in modern catalysed petrol cars. Diesel cars may smoke a little if revved, and during winter-time there will probably be condensation apparent - but walk away if you see blue smoke of any description.
3. Clatters may be heard for a few seconds after start-up, but should disappear once the oil starts to flow. If they take a long time to disappear, worry.
4. Steering should be used on full lock - both ways to check for any play or knock in the system that suggests wear or damage.
   

If you're unconvinced that everything's okay, walk away. There's plenty more cars out there to choose from. Your safety is more important than losing face, so make your excuses and leave.