Depending on the age of the car, here is my short list:

1. Look in the trunk around the spare tire for water, rusting, etc.
2. look at the underneath of the engine and transmission for oil leaks.
3. check the glass for cracks or hazing.
4. look in the engine bay for rusting, battery terminals, rubber belts and hoses, break lines for corrosion.
5. kms very important
6. service records
7. interior roof liner for water damages (sunroof or moonroof area)
8. does smoke come from the exhaust during the first 30 seconds of starting it - or after that period (white or blue)
9. engine sound OK
10. drive for atleast 15-30 minutes at different speeds and road styles, any funny noises.
11. If any doubt take it to another garage of your choice and pay them for an evaluation. Better Fr. 100 now than 25,000 and find you bought a lemon.