Never
I have been taught all my life from my father, who owns a car dealership, never to buy a new car. You lose a lot of money the second you drive it away from the dealership. I have never had a problem when I go to buy used cars because I know what to look for and where. Often there is a time of year when the new models are coming out and dealerships want to get rid of inventory. Also, sometimes people do take back a recent purchase and the dealership can no longer sell the car as new. These are two great times to buy a used vehicle.