Yep, these days a bank cheque is NOT as good as cash. The buyer can cancel the cheque on you once they drive away with your car. All they have to do is ring the bank and say they lost it and it's then canceled and you'll get no money. you then have to start the chase for your money or return of your car.
I keep the car until the bank cheque clears then they can take it, unless they pay in cold hard cash!