The dealership is putting you at risk by saying it's a characteristic of the car.. take it back up their and have them put that in writing.. ESPECIALLY if they didn't inspect it. Could be the wheels are on wrong, bad alignment, tires might need balancing.. it could be a number of things. But, TAKE IT BACK up there.. if they try to say it's a characteristic of the car tell them to put that in writing and that they didn't inspect the car for any issues. Then.. call Acura. Your car is not supposed to shake..