“payment for order flow.” As of 2010, every American stockbroker and all the online brokers effectively auctioned their customers’ stock market orders. The online broker TD Ameritrade, for example, was paid hundreds of millions of dollars each year to send orders to high-frequency trading firms, including one called Citadel, which executed a large number of orders on TD Ameritrade’s behalf. Why were these companies willing to pay so much to see the flow? No one could say with certainty.
