CarMax Inc (NYSE: KMX) posted weaker-than-expected second-quarter results on Thursday.The used-car retail giant reported second-quarter earnings per share of 64 cents, missing the analyst consensus estimate of $1.09. Quarterly sales of $6.594 billion (down 6% year over year) missed the Street view of $7.024 billion.The company bought 293,000 vehicles in total in the second quarter, a 2.4% decrease. Of these, 262,000 came from consumers (down 2.7%) and 31,000 from dealers (up 0.2%)."While this was a challeng ...