It's called "Front Running" by an MM. They buy shares for their own inventory first filling their own order (or an order from a hedge fund buddy trying to buy or cover a short position), before filling yours. MMs in the OTC, especially Pinks do it all the time. Your only recourse is to complain to your broker. It often works, too.
The other possibility is wash trading or naked shorting by an MM. Wash trading is just selling to themselves to give appearances of volume.
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