Test drive before buying. And make sure you test it in the early morning or before they start the car for the day. Touch the bonnet and if it’s cool, you are ready to test the car.
Some dealers cheat on mileage. Look at the condition of the car vis-a-vis the mileage recorded. Does the wear and tear look consistent with the mileage recorded?
More importantly how does the engine sound and how the transmission shifts after first start? Also, observe the exhaust after firing up the car to see if there’s excessive white or black smoke. If there’s a little too much smoke (especially after initial evaporation of water, which is normal) then realise that there might be engine issues like a worn piston ring or head gasket leak. You walk.
Go slow when you test drive for the first 5 mins. Transmission shifts smoothly? Then go abit faster. Check if the car drives straight on a flat and straight road by briefly releasing the steering wheel. Check for any abnormal vibrations at >80km/hr (could be misalignment of tires or more). Test drive it for at least 20mins. If they don’t allow, walk, because they probably have something to hide.
Use a used car checklist to go through items, although I usually only check the major items. Look at engine oil and transmission fluid using the dipstick. Is it blackish or dirty looking? If the transmission fluid has a burnt smell, move on to the next car.
Finally, if you can, get the car scanned using a diagnostic tool that your mechanic would have. Assuming the dealer is comfortable driving down the car to your workshop for inspection. If not, move on.
Quite a few steps to take note but these tips have helped me purchase a number of used (even high mileage) cars without much after sales trouble.
Thanks for the good tips.... Btw, how you check the ATF of those rides that do not have a lipstick to its transmission?