In the United States, the National Highway Traffic Safety Administration (NHTSA) regulates the sale of new motor vehicles. The NHTSA defines a "new motor vehicle" as "a motor vehicle that has never been sold or used (other than for demonstration or testing purposes) and has not more than 7,500 miles on the odometer."
Therefore, a vehicle that has been titled under a business but has only 400 miles on the odometer could potentially be sold as new if it meets the other requirements of the NHTSA definition of a "new motor vehicle".
However, it's important to note that there may be state laws or other regulations that further restrict the sale of new motor vehicles. As such, it is always advisable to consult with a local attorney or the local Department of Motor Vehicles for specific guidance on the requirements for selling a vehicle as new.