There are many skilled and savvy contributors to this board who know their way around a used car lot or auction site…By listing the finer points of used car buying in the real world, many readers could learn what we have learned over the years. I’ll start it off with some of the basics.
Mileage. It’s important. Nothing lasts forever regardless of salesman’s claims that certain makes of cars “are just broken in” at 150,000 miles…
How do I know if it’s been in an accident? Ask the dealer for a Carfax report…They all subscribe to that service and should be willing to provide you with one. Also, look for evidence of re-painting…You WANT to see some rock chips and dings in the usual places, the front edge of the hood for instance. Unblemished paint is a warning signal. How does the drivers seat and foot-well look? More wear than you would expect? Another red light. Anything leaking under the car? Take a look…Turn on the key and check the dash warning lights. The whole constellation should light up, including air-bag and check engine. Start the engine. Did it start normally? Did ALL the warning lights go off?
Okay, someone else take it…
Less wear than would be indicated by the mileage is a red flag, too. If there are new rubber pedal covers, then the mileage could be a lot higher than the odometer shows. Unless it’s a late model Toyota, of course. 
If the interior looks too good, ask how the car was used. It could just be that it is a commuter car and the driver was usually the only one in it. I had friends visit over the summer; we went sightseeing. Someone commented on my nice, new car. But it’s 4 years old. Too good to be true can be true under the right circumstances.
Look in the trunk and pull up the carpet. See if there is any rust or debris. Also check to see if there is a spare tire. Many newer cars have them as an option, or an older car may just not have one anymore.
I do a finger dip in the tailpipe, anything too much or black I walk away. Also looking at wear on the brake pedal is an indicator of type of mileage. Any leak is a bad leak. Check condition of all fluids!
Yes indeed…The spare tire and jack are important indicators of how the car was treated and maintained. When you find a “cream puff”, the spare tire and jack will be brand new, in their original location, undisturbed…Look at the other four tires. You want a matched set with a reasonable amount of tread…
First, car auctions are the WORST place to buy a used car. They are at the auction for a good reason.
I buy the seller as much as the car – a dumpy house in a bad neighborhood is a red flag.
I see if the owner has kept all of the service records and all maintenance has been performed on schedule.
I run the VIN thorough carfax and other services. I take the VIN to a local dealership and have them run a report.
I research prices on NADA, Kelly Blue Book, cars.com, autotrader.com to see what it is really worth in today’s economy (wholesale or trade-in in most cases).
I take it to an independent mechanic who specializes in the particular make and pay them for a pre-purchase inspection. I subtract the cost of needed repairs from the price of the car.
I take it for an emissions check and make sure it passes.
If any of the above are not to my liking, I walk away from the deal and keep looking. There are way too many nice used cars available for reasonable prices these days.
Twotone
I know at least three people that bought cars at an auction, and all were happy with them. One guy hasn’t bought a car any other way in the last 20 years. As it turns out, they all buy at the same auction.
Check the gaps of the panels. Hood to fenders, fenders to doors, doors to quarters, quarters to deck lid. The gaps cannot be perfect but big differences are not good. Check jambs for masking tape paint lines. Also look under the hood for labels. If the emission, fan, a/c labels are missing then I go to the next car.
I think a lot depends on what kind of service one wants from a used car and what one is able to afford. In some of the transportation specials I purchased, my question was “How bad an accident was the car in?” and not “Was this car in an accident?” I would ask the question, “How much oil does this car use?” and not “Does this car use oil?” I would make certain that the frame didn’t show signs of being bent, the engine block wasn’t cracked. the car steered correctly and the transmission shifted properly. I set aside money for tires and a brake job and other possible repairs.
As I moved up a notch, I would check the tires to see if the tires were all the same brand and type or at least the tires on the same axle matched. I would check the car for possible accident damage and certainly have a mechanic check the car.
At the next level, I would do everything at the previous level plus be certain that there was some factory warranty remaining and find out everything I could about the history of the car. At this level, I do consult the frequency of repair charts in Consumer Reports and look for potential problems.
At level two there are some really good buys. I remember when my mother went back to work and the family needed two cars. This was in 1954. My Dad really wanted a station wagon, but all metal station wagons were too expensive. Woodies were cheap, but needed extensive work. The Fords and Chevrolets in our price range were pretty well used up. My Dad finally came up with a 1947 DeSoto coupe with faded maroon paint that ran well for $325–about 1/2 to 2/3 the cost of a Ford or Chevrolet of the same year. That DeSoto was a wonderful car–I think the only repair it needed was a new thermostat. I was in junior high school and was put to work on the car with rubbing compound and then wax and polish. It looked great when I got finished with the job.
At any level, first driving impressions count. If the car doesn’t seem right, take a pass. If the first impressions seem good, then check it out and if it passes your check-out, pay a mechanic to look it over.
hold your hand 1/8" away from the tailpipe. if your hand gets sucked in once in a while, its got a bad exhaust valve. dual exhaust will tell you what bank its in.
if you can get a test drive, and when your out of view, floor it. one of the best ways to see if the engine is still any good.
Whenever big money goes out, the shopper should check the door wells and under the hood and around the inside of the trunk. Look for signs of repainting which looks like flat paint or “permanent dirt”. One door that doesn’t open easily is a bad sign. Don’t even test drive it.
On the test drive; if anything feels wrong or the engine or transmission goofs up at any time, don’t buy it.
If everything goes right up until now, have a shop check the car out for a pre-purchase inspection at a price you agree to before it is done.
Finally, if the check engine light or service engine soon light comes on, don’t trust the dealer to fix it before you buy it.
Newer cars “as-is”: For non-mechanics; if you can’t afford to put $6,000 into it after you buy it, you can’t afford it. If you do buy it change the oil immediately, you might get a third month out of the car.
If you are the mechanic, make your own decision.
one good reason to go with them if they want a test drive. also, one never knows who is gonna show up, they might be looking for a joy ride and ditch the car after a bit, or go steal some things and use your car to get away
Is there a service record available with all receipts and documentation?
For older vehicles especially, look for any non-factory welds on the frame, or other important members.
Look for any suspicious oil stains coming from the engine/trans, or from leaking shocks/struts
Jack up the wheels and try and wiggle them to check for worn suspension/steering parts.
If buying a used car privately, know the previous owner. Are they older, mature, retired, easy-going, neat? Or are they the opposite? Keep in mind that there are exceptions to each.
If buying a collectible or classic vehicle, make sure the numbers match. Bring a book or other resource to check the VIN to make sure it is what its supposed to be.