But TOS/ameritrade never fills below the limit. they are giving the worst price at every opportunity. TOS/ameritrade is the worst offender of this practice and they generate tons of revenue from payment order flow at the expense of their customers. I don't know about IB or other brokers.
Interactive Brokers does not sell their order flow. https://gdcdyn.interactivebrokers.c...rmSampleView?ad=order_routing_disclosure.html