The US government is manipulating the markets and insider trading like there is no tomorrow. So at this point, anybody cares? But let's say as long as the quotes are valid and from the market and the fills are also realistic, what is the difference if you lose it to the market or to your broker? Anyhow, AI says: "In general, brokers cannot directly trade against their clients on centralized exchanges due to regulations and the way these exchanges match orders. However, some brokerages may offer proprietary dark pools where brokers could potentially take the opposite side of a client's trade."