Oh, I've seen it, but not that common. It could be a brokerage with 2 different people or institutions where one wants to sell and one wants to buy.
Another trick I see is the market maker ARCA showing up on some Level 2 screens and not others. My Schwab Level 2 has ARCA on the bid at .08, while my OTC Level 2 doesn't show it at all. That's why some trades are going off at .08 when some sites say the bid is .0753. In my experience ARCA often represents overseas trading, and strange things often happen when they show up.
All part of the games they play, and make no mistake, we individual investors are at a disadvantage to the big boys.
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