Is There A Risk Hiding In Carvana Stock's Record Quarter?

Carvana (CVNA) sold a record 197,325 cars in its latest quarter. While that figure is up 38% from a year earlier, the key metric to watch is a smaller one. The profit Carvana makes on each vehicle actually fell over the same period. At 28.9 times earnings, against 21.5 for the S&P 500, investors are likely paying for profit that grows. So why is Carvana earning less on each car as it sells more.