The Online Used Car Market Is on Course to Pass $164 Billion in 2004 The U.S. online used car market is on the brink of explosive growth. IDC estimates online used car sales' share of all used car sales will jump from under 3% in 1999 to almost 40% in 2004. However, IDC warns brick-and-mortar car dealers could put up a roadblock in the market's development.