There are three different types of car dealer licenses, Class I for new car dealers, Class II for used car dealers, and Class III for junk/salvage car dealers. Mass. General Law Chap. 140 §58 details these license classes.
Class I - Any person who is a recognized agent of a motor vehicle manufacturer or a seller of motor vehicles made by such manufacturer, for the purpose of selling new motor vehicles and the purchase and sale of second hand motor vehicles being incidental or secondary thereto, may be granted a Class I license.
Class II - A person whose principal business is the buying or selling of second hand motor vehicles may be granted a Class II license.
Class III - A person whose principal business is the buying of second hand motor vehicles for the purpose of remodeling, taking apart or rebuilding and selling the same may be granted a Class III motor vehicle junk license.