Hi Nick, good question.
The most common misrepresentation seen on used caravans offered for sale is the year of manufacture and vendors often try to pass off older caravans as later models.
There is some helpful information which will help yo to determine exactly how old a caravan is
Click Here
All caravans manufactured after 1992 will have a CRiS number, this is etched onto windows and the caravan should have matching documentation with the same number on it. Vendors often come up with all sorts of excuses for missing CRiS numbers and while it's true that the caravan may have changed hands and not been re-registered the CRiS number should still be visible on te windows so if it is not, ask yourself why.
More on the CRiS HPI scheme
Click Here
There is some good advice for buyers in the Used Caravan Guide,
Click Here
Each sub heading is a link to more advice and information, click on the text.