Vehicle Remarketing Solutions surveyed 200 dealers throughout the UK and found that 97% had 'got the message'.
New legislation comes into force on February 1, which means that a car's owner must have the vehicle's V5 document to be able to tax it.
Vehicle Remarketing Solutions managing director Mike Pilkington said: 'It is clear that dealers have got the message that they will have problems retailing a vehicle without a V5.
'They should look to buy vehicles from sources that provide full documentation. We have put in place robust systems to ensure dealers receive V5s, key codes, radio codes, spare keys and a full service history wherever possible.'
Fleets have already been warned from a number of sources that they must ensure their vehicles are sent for disposal with the correct documentation or face being overlooked by buyers.
It can take up to six weeks for the Driver and Vehicle Licensing Agency to issue a new V5 document if the original is accidentally lost or destroyed.