He said they can't sell it because it had mice in it?? That sounds a bit extreme to me? I guess I can't sell my house because we had a mouse in it a couple of years ago??
Clean up the mess the mice made, try to find out where they came in and fix that and button it up and call it good...
Anyway, sounds a bit 'fishy' to me, but since you have a pretty good relationship with the dealer, I can't imagine they are trying to pull something on you??
Anyway, good luck with it, and if you can't sell an RV because it's had mice in it, then there wouldn't be many 'used' rigs for sale out there... ;)
Mitch