I understand that once a car has been sold and the car is registered with the state, it can never be resold as "new", even if has only a few miles on it. It is then a used car, and the tax credit doesn't apply to used cars.
But I wouldn't put it past the typical stealership to lie to the unwary buyer to make him think he was buying an actual "new" car.
Can you get the tax credit for each volt you buy? In other words, take your initial investment and then buy and return a volt every day for the rest of the year, and then claim you bought 160 new volts in 2012?