Hi Rim-job. flaphandlemover is correct. Commercial standby passengers are either passengers who changed their booking onto a full flight and now on first priority standby or its overspill passengers who could not get a seat due to overbooking. Eitherway a commercial standby passenger will always get priority over a Cat A standby. Positioning crew, ALT's, Cat C firm....etc will be under booked passenger totals.
In other words.....if you see the flight is fully booked and there are commercial standbys better start looking at a different flight unless first or business have the amount of seats open vs the commercial standbys, then you have a shot at the flight, but if first and business is also fully booked and there are economy commercial standbys on a already fully booked flight, turn around and walk away.