Swapping tow-bar to new car.

I have a 3 year old Jeep Patriot and I am considering getting a new Jeep Compass.  The chassis on both are identical and it is the same towbar for both vehicles.  I asked the dealer, a very well known Scotland wide dealer, for a price to swap the tow bar to the new car.  The refuse to do it because they cannot guarantee the integrity of the tow bar, despite it being fitted new by the Jeep dealer when I bought the Patriot.  Instead they are quoting around £800 for a new one.  Are they correct in doing this?

Peter