Offer Demonstration cars

Good evening, today my dealer received an offer for a new car as a demonstration car. I would get 21% discount on the list price of the car. However, the vehicle is only available from December 2018. That means I would have to wait 10 months. The car is already in the showroom, but would not be registered as a demonstration car until June and then stand as a demonstration car at the dealer’s. I find the time period a bit long, what do you think? Greetings Waldfeen