As with all cars really:
As new as possible
As cheap as possible
Full service history, independant/owner serviced is fine to be honest.
Least miles as possible
The colour you want
The spec you want
Personally I wouldn't buy a flat red car due to blooming of the paint, a metallic would be ok though.
Do your homework. Some owners can be a little optimisticÂÂÂ

with their pricing. It might be better to wait for the right one than buy one quickly and regret it.
I've had a look at your link, I'm guessing your friend has a max of 2K to spend?? Thats a shame because there are a couple that are very nice upto 3K:
http://atsearch.autotrader.co.uk/WWW/cars_search.asp?modelexact=1&lid=search_used_cars_full&make=VOLKSWAGEN&model=GOLF&variant=&keywords=vr6&min_pr=2000&max_pr=3000&mileage=&agerange=&postcode=m20+1dn&miles=40&max_records=50&
source=0&photo=1&sort=3&ukcarsearch_full=SEARCH
In particular, the last 2 on the page. I'm sure I've read that its worthwhile getting AC because the interiors of the VR6 get a bit warm due to the heat
output of the engine?? There are a couple of other good ones on there, the grey 5 door and the green 3 door look OK too.
Ebay?? Some decent looking motors on there...
Hope that helps in conjunction with the other stuff above.