make sure gearbox is resobably smooth and doesn't judder when accelerating and bumbling about (I mean quite a violent judder that you can feel thr the stick, seat, and wheel!).
check ac works if it has it (i.e run it for at least 10mins and make sure it still kicks out cold air after 10mins use).
make sure clutch doesn't judder badly.
engine doesn't overheat.
no panel damage (i/e all gaps line up and are equal, quite popular for crashed ones to make it back onto the forecourt!).
interior doesn't look like someones eaten it, especailly door plastics etc, its very annoying when you spot some massive gouge down a really obvious bit that you previously didn't spot.
no warning lights appear on dash.
bonnet catch isn't seized!!!! rubbish design on teh mk2b's that goes sideways and out of the four I've looked at (jtd versions) they were all seized up, one totally!!!
engine isn't leaking anything, small weeps are OK, large dribbles and patchs aren't.
engine doesn't rev upto stupid revs on its own.
boot release catch works
bumpers and mirrors aren't scuffed, mismatched, broken, dented. as punto's get a lot of abuse, especially in the car park from other cars, so have a really good look down each side for door marks.