I just checked my usual supplier of my vans , to get the identical van now at the same age and mileage as when I got mine is £1500 more
Most used dealer stock comes from auction. If there is plenty of vans on the auction floor, prices will be lower. If there is limited stock then prices are higher.
Auction prices tend to go down when the major commercial fleet users dispose of lease end contact vans. ( British gas, RAC, AA, etc.)
If a seller had old stock at a higher price he will do his best to sell at the higher price even if auction prices drop.
It's all a cycle of supply and demand as it is with so many other things.
I doubt any supermarket is doing bulk price reductions on toilet rolls atm.