When you buy new or second-hand from a dealer, the law gives you protection. The van must be of satisfactory quality, as described and fit for the purpose. However, if you buy a van privately, the law only requires that the van is 'as described'. The Road Traffic Act makes it illegal for anyone to sell an unroadworthy van unless they make it clear it is only fit for scrap.
If buying privately, it's wise to do your research on the seller as well as the van.
Get a landline telephone number but you should be aware that it could be for a public telephone box or might transfer to another phone. Call the number to check.
Always meet a private seller at their home address. Check that the van is registered on the V5C Registration Certificate (the “log book”) to that address and look for signs that they reside there.
If you feel unhappy with the other party, trust your instincts and walk away. Do not be tempted by that elusive bargain.
Make sure that V5C has not been tampered with and that the document is watermarked. Compare the document with another V5C or look at the V5C for your own vehicle.