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Does a market maker sell (buy) at a bid or ask price?
The everyday investor buys at the ask and sells at the bid but the market maker does the opposite This is misleading; it has nothing to do with being either an investor or a market maker. It is dependent on the type of order that is submitted. When a market trades at the ask, this means that a buy market order has interacted with a sell limit order at the limit price. When a market trades at the bid, this means that a sell market order has interacted with a buy limit order at the limit price. An ordinary investor can do exactly the same as a market maker and submit limit orders. Furthermore, they can sit on both sides of the bid and ask exactly as a market maker does. In the days before high frequency trading this was quite common (an example being Daytek, whose traders were notorious for stepping in front of the designated market maker's bid/ask on the Island ECN). An order executes ONLY when both bid and ask meet. (bid = ask) This is completely incorrect. A transaction occurs when an active (marketable) order is matched with a passive (limit book) order. If the passive order is a sell limit then the trade has occurred at the ask, and if it is a buy limit the trade has occurred at the bid. The active orders are not bids and asks. The only exception to this would be if the bid and ask have become crossed. When a seller steps in, he does so with an ask that's lower than the stock's current ask Almost correct; he does so with an order that's lower than the stock's current ask. If it's a marketable order it will fill the front queued best bid, and if it's a limit order his becomes the new ask price. A trade does not need to occur at this price for it to become the ask. This is wrong, market makers are the opposite party to you so the prices are the other way around for them. This is wrong. There is no distinction between the market maker and yourself or any other member of the public (beside the fact that designated market makers on some exchanges are obliged to post both a bid and ask at all times). You can open an account with any broker and do exactly the same as a market maker does (although with nothing like the speed that a high frequency market-making firm can, hence likely making you uncompetitive in this arena). The prices a market maker sees and the types of orders that they are able to use to realize them are exactly the same as for any other trader.