When a broker advertises “$0 commissions,” a reasonable person asks how the broker makes money. A large part of the answer, for retail brokers, is payment for order flow (PFOF) — and it is one of the most quietly consequential arrangements in modern markets.
The mechanism
When you place an order to buy a stock, your broker does not necessarily send it straight to a public exchange. Instead, it can route the order to a wholesale market maker — a high-speed trading firm that executes the trade and pays the broker a small fee for the privilege of handling that flow.
The market maker profits from the bid-ask spread: the tiny gap between the price to buy and the price to sell. Retail orders are valuable to them because they are, on average, less informed and less risky to trade against than institutional orders. The broker gets paid; the market maker gets profitable flow; you get your fill.
Where the controversy lives
The defense of PFOF is that retail investors today get price improvement — fills slightly better than the public quoted price — and pay no commission, a genuinely better deal than the commission era. The critique has two prongs:
- Conflict of interest. A broker paid by the market maker has an incentive to route to whoever pays most, not necessarily whoever fills your order best.
- Opacity. The cost is invisible. You never see a line item, so you cannot comparison-shop the way you could with commissions.
“Free” trading moved the cost from a visible commission to an invisible spread. Whether that is a better deal depends on how good your fills actually are.
Why regulators keep circling
Securities regulators have repeatedly weighed restricting or even banning PFOF, and some jurisdictions have moved against it outright. The core regulatory tension is best execution — the legal duty a broker owes to get you the best available terms — versus a payment structure that, on its face, rewards the broker for something other than your best fill.
What it means for you
For a long-term investor buying liquid stocks and holding for years, the per-trade impact of PFOF is small. For a high-frequency trader, execution quality compounds and is worth scrutinizing. Either way, the lesson is the same one this site keeps returning to: when a financial product is free, find out who is paying, because someone is.
See the glossary entries on bid-ask spread and market maker.