“”” process known as “payment for order flow,””””
Also, the way to avoid being scammed by the above process by the brokerage firms is to place ‘limit’ orders when you buy or sell.
When a person places a ‘market’ order to buy or sell, they are subject to the brokerage firm buying at the highest price offered or selling at the lowest price offered.
That may work in normal times and normal stocks but in high volatility it blows right through the limits. Then the brokerage has to figure out whether or not to buy/sell outside of the parameters you set. They have little clauses in their contract with you to limit their legal exposure on these decisions.