In recent years, the auto industry has seen record sales for new vehicles, and many have seen that as evidence of a strong U.S. economy. Yet more recently, fears that the auto boom might have topped out have hit shares of used-car retailer CarMax (NYSE: KMX), and coming into its fiscal second-quarter report on Wednesday, CarMax investors had wanted to see signs that growth might return to more typical levels. Unfortunately, the car retailer wasn’t able to deliver what most of those following the stock had wanted to see.