Jon left market making about two decades ago. The smaller MMs couldn't afford the technology of linkage and multiple list. Very different model today and just think of the cost of technology when your up Citadel, Sig and the others. Today they are mostly running volatility books in their names - not all, but most of the giants.
Generally, market makers profit by charging higher ask prices (selling) than bid prices (buying). The difference is called the 'spread'. For example, the market maker may purchase 1000 shares of IBM for $100 each (the asking price) and then offer to sell them to a buyer at $100.05 (the bid price). Market Makers in America make an average salary of $96,909 per year or $47 per hour. The top 10 percent makes over $172,000 per year, while the bottom 10 percent under $54,000 per year. You can also make a lot of money starting a blog. At https://afreeadvice.com/how-to-start-a-blog/ you can find a tutorial with advice on how to start a blog and make money in a couple of hours.
Really? Bloggers? There are Youtubers who make 100K a month. What the hell does that have to do with market-making? Please listen carefully.
Well, that is their fault, not mine! And in that one, all one has to do is listen! It's an audio thing.