Something done by Ben aka Purple pants off RSOC, been useful for a few people including me

Outside the car

-check all the wheels for kerbing
-check to how the tyres are wearing, they should wear more on the inside. if they don't the tracking needs doing. Also check the tred as that will be another £260 upwards
-check the brake discs and pads too. Feel the face of the discs to see if there is a lip.Stick your finger round the back of the disc and feel too. this would cost £300 if the pads and Discs need changing.
- see if the body work is dented/scratched. If its dry get down eye level with the car and check for dents. it will have swirls and a few marks as its a 2nd hand car. just worry about bad ones.
-look under the front bumper for scuffs and make sure the under tray is there check the bumper for cracks. £400 for a bumper!
-dont worry about stone chips this is normal as the paint is very soft.
-the paint should look orange peely if its standard paint and the rear quarters should look wavy as they are all like it
-look inside the door shuts and boot for over spray.
ask if its been in any accidents

Engine


-dont worry if its sounds tappy. they all do.
-ask what oil he uses. should be 5/40 or 5/30.
-Ask what fuel he uses. If he uses normal fuel. Walk away! it must have 97ron in it. ie super unleaded/vpower
-check there is a white shield over the turbo at the front near the slam panel. if this is missing its another £80.
-next to the brake reservoir is the chargecooler reservoir. when the engine is running take the lid off and make sure there is a stream of water squirting out of it. if there Inst. ask when the last time he check it was. if its more than a day walk away. this not working can cause serious damage.
-check the thermostat housing for pink crusty stuff around it (this is in front of the coil) if this is leaking thats another £50.
-look at the coolant tank. if it looks cloudy. possible head gasket failure.
look under the oil cap for a creamy/mayonnaise gunk. this means the head gasket has gone. walk away
-when the car has been driven and is warm. One of you rev is up to 4k the other one watch for smoke. A puff when you back off is fine as long as it black. anything else is going to be expensive.
-when the cars warm. put it into 4th raise the revs till 2k rpm. then lift the clutch it should stall if it doesn't the clutch is slipping. this will cost £500.
-drive the car slowly and turn the wheel quite far. like your driving out of parking space. listen for a knocking. this could cost you upto £150
- The boost if its standard should hit the white and then back off. test this is 3rd gear. it should be at full boost by 3000k RPM. If its miss fires/holds back when you accelerate at 4000 to 5000RPM dont worry this is the MAP it can be sorted.
-check the chassis number with the number on the side of the head. make sure they match.

Inside the Car.


-Dont worry about creased seats. just check for tares and rips.
-check the carpet on the passenger side nearest the centre of the car at the top to see if its wet. its its soaking you make need a new carpet. about £100. plus pollen filter and seal
-check the steering wheel for wear. £130 if its worn alot. the blue normally comes off.
-Check the boot well, for water. make sure its not rusty.
-make sure it has the RS leather Wallet with it. If it hasn't knock him down £100.
-make sure it has a full service history with receipts.

All the prices above are ford prices and parts can be got alot cheaper on the rsoc so dont worry to much about running/ servicing costs then obviously all the usual stuff when buying a car