For normal stocks like Apple, etc, yes they have a dozen MM so you will get a good picture. On a stock like GNBT, absolutely not. That is why you see $0.04 spreads or the next lower bid is $0.02 lower. Level III would show if the best (primary) MM has more bids just below the best bid.
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Generex Biotechnology Corp. (GNBTQ) Stock Research Links
Disclaimer: Of course, all of this is my opinion and you should not make any investment decisions based on my opinion. I have not received any non-public information.