I've non-rev'd recently and in one instance a paying passenger showed up after the doors were closed and we were still at the gate but they did not pull anyone off because the doors were closed (the husband was on the phone with her and was not happy). Then on the return flight, 3 people didn't show up for an oversold flight and as the gate agent was taking us down the plane told the other guy to close the doors just in case the people showed up.