To the best of my knowledge there is no legal requirement to list the vehicle's VIN, and although there is provision on the listing page to do so, according to the following help pages, it is not required.
Always best to provide a VIN number, so that people can check the status of a vehicle prior to bidding or purchasing. I personally will not entertain a vehicle without the VIN number. Too may dodgy people trying to swindle through wrecks
