Check your state laws on "curbstoning" as it's illegal in many states. The number of vehicles you can sell without a dealer's license will vary from state to state. Here's what you can do in Washington State where I reside. "Washington law defines curbstoning as a person or firm selling five or more vehicles that are each less than 30 years old in a 12 month period. Under state law here, you can sell up to four vehicles that are registered in your name in a 12-month period. So once you sell any vehicle that’s not registered to you, or if you sell five vehicles or more, then you’re in violation of the statute".
"The most-common violation is people who sell cars without ever putting those cars in their name. They never transfer the title. The typical curbstoner buys a vehicle and gets some paperwork in lieu of a title, and then just passes it on to the buyer. They never have the vehicle registered in their name".