Sales of certified used vehicles have increased 46% since 2000, with certified used vehicles comprising an estimated 35% of late-model used vehicles sold in 2002, according to the J.D. Power and Associates 2002 Used-Vehicle Sales and Certification Study released Tuesday. The inaugural study measures the satisfaction and experiences of owners of certified used vehicles. "Certified" refers to late-model used vehicles that have typically undergone a detailed inspection at the dealership and are sold with manufacturer-backed warranty coverage.