Compression test on a good engine should give results somewhere between 150-170psi and all cylinders should give fairly similar numbers. see this thread for example:
http://www.skylinesaustralia.com/forums/in...=136725&hl=
So first of I would be asking to see the results of the compression test as 20psi isn't correct. Also find out what he means by "he said its a double wheel and it can be repaired" if one or more of the wheels are buckled even though they can be fixed it's a major pain in the ass as fixing them doesn't always help that much, normally the steering wheel will vibrate round 80-120km/h depending on how bad it is.
As for the k's completley ignore them, they are never correct. Look at general wear and tear on the car, drivers seat on the door side, carpet around the clutch and accelerator pedal, the plastic around the bin in the drivers door arm rest, the material on the inside of the bonnet and the condition of the paint on and around the engine I always find are good indications of the cars use.
Otherwise car looks good, just do some bargning to get the price down a bit