Back to the dreaded MMs shaking those weak hands? If the price of the stock goes down, and some individual investor wants to buy, who is obligated to sell to them? As in make the market? Who is obligated to buy at a higher level if there are no buyers?
The typical way they make money on the big board is to shave off factional pennies on the difference between the bid and ask. But you need volume and rapid frequency of trades to make money by following that scheme as a Specialist or MM. I can count the trades as dots on the LLEG chart.