Currently dealers are looking for gross margins of £4,000 to £5,000 on recent vans but the bottom has dropped out of the caravan sales market and willing buyers are very scarce. The reason dealers are asking such high prices is because they're trying to get the same income to cover costs from fewer sales. Unfortunately for them that plan can't work because higher prices means even fewer sales. The trouble is that lower prices to increase volume doesn't work either because there just aren't enough punters around.
Buying from a dealer gets you cover under the Consumer Rights Act and you can reject the van inside 3 months and get your money back. After that you have to give the dealer one chance to repair a fault and if not satisfied you can reject the van but
the refund will be adjusted for use.
On a private sale you're on your own with the seller having no liability.
Best advice is get an independent caravan tech to look over the van to avoid a lemon.