IRS or not... many states have laws that require sales tax on the actual value of the vehicle if the sales price is below that. So if the Blue Book value of the car is $20,000, 8% sales tax is $1,600. Still a bargin, but much more the $20.
Our state changed how they do things. They used to accept $1 sales for vehicles. Now they set a limit on how low a vehicle can sell for. Don’t recall but think at $100.