Part-exchange prices

I have been to a dealer to buy a new motorhome on a cash + part ex basis. He is offering a good price on the new vehicle but I feel he is trying to rip me off on the part ex price. I have a 2005 1 owner low mileage CI Carioca 625. He has an identical model on sale on the forecourt which is 54 reg at £19000 so how can he fairly offer me £10/11000 for my vehicle. There is nothing wrong with the vehicle other than superficial minor items as I have annual habitation/mechanical work. So even if he spends £1000 to put it on the forecourt he makes 7 or 8000 profit - is this normal or shall I tell him to go boil his head?