Well one thing is for sure, there are no shares for sale at all. This tactic of filling only 300 shares of an order is to discourage people from buying, as they will get charged the full commission even if the order isn't completed.
Granted not all brokers do this, but Schwab which I use do and many others do as well.
Granted not all brokers do this, but Schwab which I use do and many others do as well.
2