It has been explained to me that for a retail investor to get a trade to execute he needs to sell at the bid and buy at the ask. you can put in an order the opposite way but it may not go. If you put your order in the way I said, it goes immediately. Only the MM's get to buy at the bid and sell at the ask. We are at their mercy. Usually when you are making a trade you want it to execute right away, so that is why people sell at the bid. I can't tell you how many times I have put an order in to sell at the ask and it doesn't ever go, then the stock drops and I am in the crapper. It only works the other way if the stock is on the rise, which is usually not when you are going to be selling. Like I said at the beginning, this is how it was explained to me in very simpe terms. The whole mechanism is actually much more complicated than that, but I don't understand it well enough to go into at depth. Let me know if I am wrong, as if I had to ask.
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