In the example above, if they had not filled your order at the price improved price, it would have either filled at the higher price, or rested at the higher price.  In either case you get a higher price.<p>They do this because they are taking on the risk that the market will <i>eventually</i> allow them to work out of their short position at a better price than they paid you. But they don&#x27;t <i>know</i> that it will do that.<p>One of the reasons they pay for retail flow is that it on average goes back and forth, making it more likely that this trade works to their advantage.<p>None of the profit of that trade came from you the limit order provider.  It came entirely from the average spread.