I’m in the process of buying a car and would really like to know this 
You look for scars, bruises, etc.
wise ass 
Ummmm…
What does “flogged” mean in the context of purchasing a car? The only sense that I’ve seen the word used in is the one that Badtz alludes to. I’m assuming from your answer that that’s not the correct definition.
Maybe I just have a blind spot, but I suspect that “flogged” is not universal slang for whatever it is that you’re using it for.
Stolen? Crashed?
I fired up my translation program earlier on to answer this. I’m glad to see the natives are having some problems with it too. 
Do you mean ‘flagged’ - as in previously the vehicle was in an accident, flooded, totaled, returned under a lemon law or anything that the buyer shouldbe made aware of? A little clarification would certainly help us help you.
“Flogged” is going to mean either stolen or driven into the ground, depending on the OP’s country of origin.
Two quick checks that may seem obvious-
Use a magnet in proportion to the cost of the car. That is, if you are picking up a ’92 Civic beater car, don’t spend too much time with it. Just hold it up (cover it in a small scrap of cloth first to protect the owner’s paint) around the wheel wells and next to the frame. If there is a quantity of plastic there, then you’ll feel the difference. On more expensive cars, take more time to look for dents that were pulled or rust that was filled.
Next, keep a keen eye for paint. Sure, a blue fender on a red Ferrari stands out, but look for feathered/ blended paint moving from panel to panel. Open the hood/ trunk and look at the paint on parts that are difficult to access. Check out the color of parts like the lower radiator supports. Even if a shop took the time to paint them, they still won’t quite match the rest of the interior.
No much, but at least we’re headed back to the OP.
Good luck.
(slight hijack)
IMHO Award for best car-flogging scene:
John Cleese in the Duck Dinner episode of “Fawlty Towers”.
“Duck’s off!”
There’s no really foolproof way to tell if a car’s been
abused. There are a couple of things you can do, some
trivial and free, some less trivial and more expensive.
First of all, the easy stuff.
- Pull the dipstick and check the oil. It should
not be any lower than a teeny bit below the low mark.
Wipe some on a white paper towel and look at it. If it’s
really light brown/golden then they probably just
changed it. This can be good or bad - they were smart
enough to change the oil, which means they probably have
some basic knowledge of engines. But it could also mean
that they hadn’t changed the oil in 9 million miles
previously and knew they better change it.
If the oil is really “midnight in alaska” black,
then they probably haven’t changed it nearly recently
enough. Ask them when the last oil change was, and if
they’ve been following the manufacturer’s recommended
oil change intervals.
Optimal is when the oil is golden brown with a little
to a fair bit of black in it, and slightly transparent.
This usually means it’s been changed fairly regularly,
but not two minutes before you came and looked at the car.
Brown, opaque oil, the color of milk chocolate, is bad.
This is oil that has coolant in it and usually indicates
a blown head gasket. Also, the oil shouldn’t reek of
gasoline. It can smell like gasoline a little bit, but
it shouldn’t hit you in the face with gasoline smell.
-
Maintenance records. Do they have them? Lots of
them? If so, you’re likely to be dealing with a careful,
methodical person who takes good care of their car.
Appeareance of the car can also help, but don’t take it
as sacrosanct. Everyone takes their car to a detailing
place to have it cleaned up all pretty before they try
and sell it. -
Ask them why they’re selling it. There should be
a fairly straightforward reason. If they’re evasive
or can’t seem to really tell you why, get suspicious.
Less trivial stuff:
-
Test drive it. Start it after it’s been sitting
for more than 8 hours. Does it start easily even when
cold? When you drive it, does it shift easily? Notice
any strange vibrations or weird behavior that would not
be attributable to normal differences between cars?
There’s lots of little things you can look for - pick
up a Consumer Reports magazine issue on buying cars.
They have lots of good tips. -
I HIGHLY RECOMMEND THIS FOR ANY CAR PURCHASE: Make
an appointment at a competent mechanic and have the
mechanic inspect the car. You can even take it to a
dealership and tell them to do the same inspection they
would on a trade-in car. This will cost money, of course.
Ask them how much beforehand. But they may be able to
give you a multi-page checklist of things they checked
and what the condition was. If the owner will not consent
to letting you have the car inspected, then RUN away.
They are trying to hide something. I did this for my
300ZX and although it cost $200, it was well worth it.
-Ben
Another thing you may want to look into is getting the VIN checked to see if the car has been reported as a flood loss or totalled by an insurance co or some such. This depends on who you’re considering purchasing from but some curbside dealers will buy junked cars from another state and then fix them up enough to run and sell them to unsuspecting buyers.
Check out http://www.carfax.com or http://www.e-autohistory.com or similar sites for more info.
CarFax can tell you if the vehicle incurred significant damage, if any state listed it as totalled/unsalvagable, and will help identify if the odometer reads what it should.
Ask if they can do a compression test. This will tell you the general condition of the engine (specifically the piston rings). Low (i.e. below spec) compression is bad; it means the rings are worn, your power output will be down and you’ll be looking at an engine rebuild soon. A little wear is expected on older cars; your mechanic should be able to tell you if it’s comparable to the car’s mileage. Also, if you have the opportunity to start the car when it’s cold, check the exhaust when you start it and look for bluish smoke. This indicates that the car is burning oil, another symptom of worn rings.
Check the fit of the various body panels; for example, make sure the spaces between the fenders and the hood are the same width on both sides. Do the same for the doors and the trunk/hatch/boot. Differences can indicate that the car was in an accident and was repaired. If the car has been repainted, ask why - I’ll usually avoid repainted cars because rarely is an aftermarket paint job as good as the factory’s. It’s also another possible indication of a past accident.
If the car is more than a couple of years old and the engine compartment is spotless, be wary - it’s possible the seller had the engine steam cleaned to hide a leak (such as a head gasket leak - another expensive repair). Ask when the timing belt (assuming the car has one) was last changed - this can cost several hundred dollars, and should be done after every 50-60k miles (depending on manufacturer).
Don’t forget the small stuff which you may forget, such as the heating/A/C - it’s expensive to repair. Turn the heater fan on medium, crank the heat up, and see if you smell anything unusual (a sweet smell) - this can be indicative of a heater core leak.
It might not be a bad idea to make up a checklist, print it out and bring it along so you don’t forget anything. It’s easy to rush through and miss stuff when you’re checking out a car.
even fresh oil in a bad engine will smell burnt. Check the automatic transmission oil. Clear, pinkish–good. Anything else–bad.
Push down on all four corners of the car and release. It should pop back up and return about halfway. More that that or less than that–bad struts or shocks. Look at the struts. Any oil or oily dirt means you’ll have to replace them.
Turn on the radio. Punch the presets. Rap or teenybopper rock are bad news. National Public Radio is an indication that it was driven by someone who listens to car talk.
Dirt or wear on upholstery–the person had no pride of ownership.
Find out when the timing belt was last replaced. subtract that from the mileage and divide by 50,000. ANything in excess of 1.00 will mean it’s overdue for a timing belt and the water pump is about to go. $500. If it’s close to or greater than 1, get the seller to knock 500 off the price.
tire wear–obviously, you want to know if you’re going to put a couple of hundred into new rubber. But also note uneven wear caused by failure to rotate the tires or misalignment. These indicate a laisez-faire attitude toward maintenance that will show up elsewhere.
Another simple and easy way to determine if the mileage is correct. Look at the wear on the break and/or clutch pedals, if the rubber on the pedal is worn down to nothing around the edges but the odometer reads 12,000 miles - something is VERY wrong.
If the car looks good to you then I second the opinion of everyone above, take the time to have a good mechanic check the car out.
Good Luck!