First off, ask if the car has had it's headgasket replaced once in it's history and if possible if it had the MLS (Multi Layered Steel) gasket fitted, if not, don't be alarmed, but always best to check,
Also if you have the oval fob then the car has the newer system, make sure all the electrics work as they should, windows, mirrors and the like, fogs come on etc, water ingress on the body control unit which controls all these functions is a common problem.
1 - Check the coolant tank for any signs of contamination such as oil deposits, it should be clean.
2 - Check under the oil cap for any signs of mayo, also check the dipstick.
3 - Turn the ignition to number 2 and make sure the SRS light and ABS (if the car has it) turn off after a few seconds, also make sure the fuel pump primes as well.
4 - Check the manifold gasket, make sure there is no signs of leakage around it.
5 - An easy fix, but worth checking anyway, make sure all fan speeds work, 1 and 2 sometimes pack up due to the infamous resistor behind the glove box
6 -Start the car, make sure it ticks over ok, no coasting, check for any signs of rattles, sometimes you'll hear a slight tapping noise, it's common on the K-Series, check to see if it persists though, normally should go away after 30 seconds or less.
7 - Make sure the gears all engage properly.