So if someone's buying a stock, the market maker actually takes a short position to make it available to the buyer? I was under the impression that market makers are just connecting market and limit orders with each other, is that not the case?
It's really complicated and I don't want to go into too much detail, but no, a market maker isn't "connecting" limit orders. A market maker is a market participant, just like me or you (well, sort of). They buy things and sell things, they don't have magical powers.
People get confused, but most hft firms utilize market making strategies. A market maker is just someone who puts limit orders on the book (making) vs taking liquidity off of the book (takeout). Anyone can be a market maker, and many firms do both market making and taking.
No, the exchange already matches a buy at market order to the best limit sell. A market maker is who is filling up the order books with offers to buy and sell at different prices under the hope that a regular trader will come in later with a trade the other direction at a better price.
