There is no such thing as a free lunch they say, and that rings true in trading. Brokers have costs and they need to meet those costs somehow, whether that is through the spread and/or commissions or trading against their clients via B-book. Where brokerage services are offered free, for example, in trading US equities, the broker is paid by a market maker or high-frequency trader for their client’s order flow. The adage that if something looks too good to be true then it probably is, remains good advice.