i import jap cars and am around cars all day long so i have a few points.
if some muppet came up to one of my cars with a fridge magnet he would get asked to leave. (it scratches the paint we so lovingly polish)
if some muppet started tapping on panels with his knuckle he would get asked to leave (it can put small dets in the crappy 0.5mm panels the japs call 'steel')
if some muppet tried to rev a cold engine up to 3/4 revs he would be ejected from the building forceably
the best test on an engine by far (without tools) is simply letting it warm up, stick your face next to the inlet manifold and rev the car up and down from idle to 1500rpm. most scarry noises can ONLY be heard at low revs, other engine noises get covered by induction and exhaust noise. rev it slightly, then let it drop down by itself, then again, and again. each time move your ear to different spots on the engine. if there are severe tapping noises, boiling, clicking or squirting then maybe consider rebuilding costs.
take off the oil cap and check for white sediment. could mean there is water getting in the oil somewhere, or even that the engine has been sitting for a long time without being started. which also goes in your favour cos' the guy selling may be more keen to get rid of it.
check color of coolant. get the light behind you and see if you can see 'pretty rainbow colors' in the water, if so it may have oil in it. might be serious, might not be.
check the color of the oil on the dipstick, trans fuid if auto, power steer fluid, start car and turn steering wheel sharply lock to lock to see is steering makes a stupid squeel kinda noise.
pump the brakes till its got full pressure and hold your foot on it to see if it holds, then check master cylinder for leaks. if auto, place the car in D and stall it up to 1800 rpm and listen for clunking or knocking under the car, could be worn trans mounts/ engine mounts if it makes a thump. slowly go through all gears to check their engagement. they should not rev freely then thump into gear. could be a sign of worn trans or idle set too high.
common sense is the best way to check for accident damage. look at the color of the car first, if it is slightly different, then it probably is different, as was mentioned check all the painted bolts you can find, if they are chipped/different color/rusty then the panel has been off, and the simplest way is to look straight on at a suss panel with the light reflecting off it into your face. if it seems like there are imperfections UNDER the paint like scratches, swirly little circles, peel, bits of sh1t etc then it HAS been painted.
jap production lines use robots to paint cars. there are never runs or imperfections. NEVER. i assume australia uses robots too.
ayway my only specific advise to buy a vk is to check the parcel shelf by sticking your head in the boot and look underneath. they love to rust there due to crappy window seals. (i didnt do this, now i gotta fix it)
anyway, my final point may not be relevant to newer cars, but it is this; a vk commodore is 25 years old now. any which way you look at it its gonna cost you money, everyday, every week, every year until it is scrapped. they are gonna rust and they are gonna be painted somewhere. they are gonna misbehave when you least want them to.
lol. hope this may be helpful to someone.