Firstly I think servicing/service history is very important, check the age/mileage of the van and make sure any appropriate big ticket service items have been done like cambelt/water pump/DSG service as they can be pricy to do
Secondly if you are intending to buy it spend a bit of time in and around the vehicle and have a proper look at everything, bend down and check the lower areas and wheels etc, stand on a tyre and have a look over the roof, then spend a bit of time sat in it and check everything is present and correct, make sure all functions and options are working, things like aircon/heaters/heated seats etc etc
Its easy to get excited and caught up in the moment when buying something you want, after a while looking at the van i tend to ask the salesman to leave me alone for a while to have a proper look or ask them if you can have a cup tea things like that, take your time and try and be objective, if your in any doubt or have any niggles then dont rush to hand over your money, ask questions and find out the facts and details before committing the cash !
