In a recent paper (Lemons hypothesis reconsidered: An empirical analysis) in Economic Letters, Arif Sultan sets out to test this idea. He argues that used cars, if inferior to new cars, would require higher maintenance expenditures. His paper tests the hypothesis that there is no difference in the average maintenance expenditures required for cars acquired used and those acquired new.
The results he gets show that there is no evidence that cars acquired used required more maintenance expenditures than those of a similar age acquired new. The conclusion to the paper reads, in part,
The purpose of this paper was to examine the difference in the quality between cars acquired used and those acquired new. I measured the quality of the car by using maintenance expenditures incurred on a car [... ] I found that cars acquired new required the same maintenance expenditures as those acquired used, all else being equal, implying that cars acquired used are of same quality as cars acquired new of a similar age. If cars acquired used were of lower quality, they would have required more maintenance expenditure.Update: The Visible Hand in Economics comments on The lemon hypothesis vs evidence and points us to other comments at Division of Labour and Marginal Revolution.