white smoke? indicates piston rings are worn... not a good sign
good way to see is get him to start it cold, say when u want to see it dont run it before u get to his house, so u can see what its like to start
see how long it takes to start the car with the key, if it turns over for ages to start its not a good sign, a quick ignition is a good sign
when the car is running when warm, open the oil filler cap and see if any blowby is coming out, maybe get ur mate to rev the engine a bit to see the blowby, blowby is bad
check the chassie for cracks and suss repairs
check the sump for bog (if people stack over a gutter, they might bog the sump up to hide damage, ive inspected a car with this done to it)