The High-Speed Trading Behind Your Amazon Purchase

I wanted to buy some mini marshmallows recently, so I went on Amazon. Perhaps because of their resemblance to packing material — light, bulky, ubiquitous — I figured they’d be cheap. But when I found the most popular brand, not only did the marshmallows cost twice what I’d pay at my local store, but the price had skyrocketed overnight.

Source: The Wall Street Journal