The used vehicle retailer underwhelmed with its latest quarterly update.Shares of CarMax (KMX -0.42%) are down 11.7% this week as of Thursday's close, according to data provided by S&P Global Market Intelligence, after the used vehicle retailer announced disappointing quarterly results and delayed a key long-term vehicle sales target.On CarMax's underwhelming quarterFor CarMax's fiscal fourth quarter ended Feb. 29, revenue declined 1.7% year over year to $5.63 billion. On the bottom line, that translated to ...