I can understand how they can make money on market orders but I just wonder how they can make money on limit orders buying at the current bid and selling at the current offer.
They collect the ECN fees, for providing liquidity instead of passing it onto the customer. For market orders they sell it to firm that wants the order. They get to jump the visible queue by giving a subpenny improvement. If your a market maker. It’s a tool to work your exposure and spread.