I think Chris hits the nail on the head here. Why would a Nissan dealer give someone else a potentally profit making vehicle when they could keep it themself. Generally speaking, main dealers cars have to meet quite stringent requirements from bodies such as the MAA and the manufacturer for which they are a franchise when selling used vehicles.
The exception to this of course is if you were looking at a private sale from a member on this forum then there is likely to be some threads that would provide you with some insights into the condition, etc, of the car.