35 ILCS 120/1c
A person who is engaged in the business of leasing or renting motor vehicles or, beginning July 1, 2003, aircraft or, beginning September 1, 2004, watercraft to others and who, in connection with such business sells any used motor vehicle, aircraft, or watercraft to a purchaser for his use and not for the purpose of resale, is a retailer engaged in the business of selling tangible personal property at retail under this Act to the extent of the value of the motor vehicle, aircraft, or watercraft sold. For the purpose of this Section "motor vehicle" has the meaning prescribed in Section 1-157 of the Illinois Vehicle Code, as now or hereafter amended. For the purpose of this Section "aircraft" has the meaning prescribed in Section 3 of the Illinois Aeronautics Act. For the purpose of this Section, "watercraft" has the meaning prescribed in Section 5-5 of the Watercraft Use Tax Law. (Nothing provided herein shall affect liability incurred under this Act because of the sale at retail of such motor vehicles, aircraft, or watercraft to a lessor.)
35 ILCS 120/1c