Actually, the 'Standby' list that you guys see contains both revenue AND non-revenue pax. No way for you to tell the difference, with the exception that revenue standby will always be above the non-revs on the list.

We (as employees) have the ability to access another list which shows the number of revenue vs. non-revs for a given flight.....which I can then look at the monitor and figure out that say the top four names are rev, and anyone below that is non-rev.

With respect to the OP....non-revs are ID'd on the passenger manifest and F/As know who is who. Anyone (rev or non-rev) can be reported through gate agents, supervisors.....law enforcement....as the situation warrants. In theory, people can indeed have their travel privileges taken away.