No son de segunda mano, sino partes nuevas que no fueron fabricadas por el fabricante original del vehículo.

Wikipedia:
The automotive aftermarket is the secondary market of the automotive industry, concerned with the manufacturing, remanufacturing, distribution, retailing, and installation of all vehicle parts, chemicals, equipment, and accessories, after the sale of the automobile by the original equipment manufacturer (OEM) to the consumer. The parts, accessories, etc. for sale may not be manufactured by the OEM. According to a report by the International Trade Administration in the Department of Commerce, "Aftermarket parts are divided into two categories: replacement parts and accessories. Replacement parts are automotive parts built or remanufactured to replace OE parts as they become worn or damaged. Accessories are parts made for comfort, convenience, performance, safety, or customization, and are designed for add-on after the original sale of the motor vehicle."[1]