What's going on?

Shares of the largest American used-car retailer, CarMax, zoomed up by 13% to an all-time high on Friday, as the company reported better-than-expected quarterly results.

What does this mean?

For the quarter ending in May, CarMax�s sales grew by 5.5% and profits grew by almost 13% versus the same time a year ago. The growth was helped largely by wholesale (selling in bulk to other businesses) car sales � perhaps as other companies step in to replace Uber�s shuttered car leasing program � which more than offset declining sales at dealerships open for at least a year.

The company said that it sees a recovery in vehicle sales on the way (from last year�s dip), which � coupled with its falling cost of buying used cars � should boost sales and profit growth in the future.

Why should I care?

For markets: Encouraging signs about the middle class consumer.

Investors tend to look at CarMax � and other used car companies � as an indicator of the strength of middle class consumers [tweet this] (since they�re probably doing well financially if they�re buying more cars). CarMax�s results are likely encouraging, as consumers may have only just started to spend the money saved from recent tax reform � growth in retail sales started slowly this year but picked up recently.

The bigger picture: Import taxes may spell an even brighter outlook for used-car companies.

On Wednesday, German automaker Daimler (they make Mercedes-Benz cars) said its annual profits will be hit by trade tariffs between the US and China. If car makers sell fewer new cars as a result of higher costs, which will likely translate to higher retail prices, more consumers may turn to used cars � driving growth in the sector higher, along with the stock prices of CarMax and its competitors.