When buying cars on eBay, you could be buying from a dealer or an individual. The difference is that a dealer makes a business out of selling cars. Therefore, they are usually registered for a business tax with the state, and they will add this into the cost of the vehicle to prevent them being out of pocket. However, if you are dealing with an individual seller, this is someone who is likely to sell a car once or twice in their lifetime as they upgrade or downgrade to a different car. It is the responsibility of the seller to register the extra income they have received from the car, as being taxable.