Manipulation and "games" played here are done by traders :-)
There are instances where orders are not shown i.e. conditional orders (AON etc,), insufficient size at a particular price point, and the one that really counts where a customer doesn't want his order size displayed--this causes the most angst as there appears to be an infinite # of shares available until he is done...
remember a couple of months back?--several MM's (I believe NITE and CSTI) only displayed sizes of 1...a call to FINRA hopefully solved that for good :-)