There is no way for you to know which MM took which tranch of your order. But one thing is for certain - the spread is the law. MM's are not allowed to buy or sell outside their spreads. They can change their spreads, and they do. But remember, it is not people, it is computers only. It is a mathematical program that adjusts spreads as needed to do business. So, NO YOU NEVER GET SHARES 'AT THE BID'. You get them at the offer of ONE or more of the MM's.
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