In no particular order:
1.) Full VW Service History - cambelt should have been changed so ask for them to do it if it hasn't been already
2.) starts first time from cold
3.) idles ok with no odd noises or splutters
4.) no oil patches on the ground beneath the engine
5.) check body work for dents and major scratches - this will involve multiple walk rounds the vehicle - take your time, it's amazing what you can miss on a first look
6.) check rear lights and rear brake light for unsightly condensation
7.) white worm on alloys and VW badges
8.) rust under wheel arches
9.) when test driving check car doesn't pull noticeably left or right under acceleration and that it brakes in a straight line
10.) No cabin rattles when going over bumps
11.) check the all the electrics work including air con
good luck and don't rush into things
