Using that same example, perhaps you place a limit order to buy one Bitcoin at $12,000 (at most), and the lowest seller is selling one Bitcoin at $11,000.
Using that same example, perhaps you place a limit order to buy one Bitcoin at $12,000 (at most), and the lowest seller is selling one Bitcoin at $11,000. In this case, your order will be instantly fulfilled at $11,000. You will be removing orders from the exchange’s order book, so you’re considered a market taker.