Wow! That's a big ask!
Don't view a van other than at a dealer of the owners home - never at a storage pound or at a (e.g.) 'service station mid-way between us'!
There are loads of used van's out there, so be prepared to walk away! You will find some cherished pristine vans, but beware of the lemons - hence your request!" You can expect some wear and tear from the use, which may include some minor dings to the sidewalls and commensurate internal signs, but nothing broken or ugly! You should be able to operate the appliances, run the taps, slide the loo in and out and check all the locks, open and close windows.. Use your nose - expect a fresh van!
You may get a feel for the seller - but my experience when we bought our last van was that some are 'economical with the truth'. A simple example was 'we never let the (HUGE!) dog in the van', but as he opened the door the dog was first in and promptly curled up between the bench seats - a creature of habit!
A service history would be good, especially if it included a damp report, usually denoted by circular dated sticker on the drawbar cowling. There is no requirement for servicing so you may find some that have not been professionally checked for years! Tyres should never be more than 7 years old, preferably 5, and carry a date mark - a pair will probably cost about £90.00.
Also don't forget to consider the cost of peripherals which may/may not be included in the sale - aquarolls or similar £100 a pair, battery similar price etc.
In the end we bought from a reputable dealer with excellent warranty and a complete starter pack having been somewhat disillusioned with several that we viewed privately. We have received excellent service either in person or over the phone if we needed help.
Very best of luck and enjoy!