Check that ALL the required service items have been completed. Although it has only done 20,000 miles there are some substantial service items that have Time or Milage requirements.
eg: Cambelt & Waterpump, 4 yrs or 80,000 miles
DSG oil change, 2 yrs or 60,000 miles I think
Brake/Clutch fluid 3 yrs
Haldex, if 4 Motion, 2 yrs
Check with VW for actual requirements
Brake Pads and Disks should be examined carefully as there is a possibility of corrosion having not been used very much.
Low milage vehicles seem good but these are commercial vans and standing around could be problematic so check carefully or you could have some hefty bills.
If the above service items have not been done then negotiate hard so you are not left out of pocket.