In the WSJ, Alexander Osipovich writes,
The practice, in which high-speed trading firms pay brokerages for the right to execute orders submitted by individual investors, has long been controversial. Some say it warps the incentives of brokers and encourages them to maximize their revenue at the expense of customers. Supporters, including many brokers and trading firms, say it is misunderstood and helps ensure that investors get seamless executions and good prices on their trades.
In theory, there are two types of market-makers in securities markets: brokers and dealers. A broker connects a buyer and a seller. A dealer buys some securities from a seller, holds them in inventory (maybe for just a few seconds), and then sells them to a buyer.
Most real estate transactions are intermediated by brokers. The broker finds a buyer for your house, and then you pay a hefty commission to the broker.
From time to time, an entrepreneur will try to operate in the real estate market as a dealer. The company offers to buy your house, with the intention of turning around and selling it. Instead of charging a commission, the firm tries to buy your house at a price somewhat below the price at which the firm expects to sell it. You save the commission, but chances are you do not get full price for your house.
It sounds to me as though the “payment for order flow” model is one in which brokers hand off customer orders to dealers. The dealers pay for the order flow because they are efficient at doing what they do, so they make more profit if they have more business. The dealers supply liquidity in the market. This enables the brokers to allow customers to trade without commissions.
Some retail investors also supply liquidity. If you target a stock at a particular price, but you don’t care when you get it, then you place a limit order. You supply liquidity, and you make it easier for brokers and dealers to do their job.
On the other hand, if you want the stock right now and you don’t care what price you pay, you are a demander of liquidity. If I am trying to arbitrage the options market by writing a call option and buying the stock, then I am going to demand liquidity. I don’t want those trades to take place at different times.
My guess is that the action in GameStop involved a lot of traders who were demanding liquidity. Amateurs buying call options and bidding up those option prices, leading arbitrageurs to want to write calls and buy the stock with rapid execution in order to arbitrage and discrepancy between call option prices and the price of the underlying stock.
The cost of operating as a dealer rises when prices become volatile, because your risk of keeping an inventory of shares goes up. This increased cost has to be passed on to traders in volatile stocks. The zero-commission model may not necessarily be sustainable in those cases. Shutting down trade for the retail investors seems like a bad solution, though. Charging a commission would be better.
When someone proposes something like “Ban short-selling!” or “Ban paying for order flow” I suspect that they are either are shilling for a trade group that stands to benefit from such a regulation or that they are just posturing without any sense of what sort of Chesterton fence they may be tearing down.