A scoring model would be nice. Each time an attendee shows up, they get points. The earlier they RSVP, the more points they get. If they cancel, the closer to t

A scoring model would be nice. Each time an attendee shows up, they get points. The earlier they RSVP, the more points they get. If they cancel, the closer to the event, the more points they lose. If they're a no show, they lose lots of points. If you have attendees who have been good about showing up but something happens and they miss an event they RSVP'd for, their accumulated past points keep them from looking bad. For events that are scheduled far in advance, people with more points can RSVP before those with less points if the organizer desires. The organizer should be able to manually override points given or taken away to deal with exceptional circumstances. You don't need to make the points visible to the attendees, just to the organizer or maybe make that an option. Since this involves people actually showing up, it's less likely anyone will try to game the points system like on Reddit. You might want to do meta points too so a user who is a chronic problem in various groups is shown as unreliable to organizers in new groups they join. That also goes the other way, making users who are good attendees in their groups look good starting off in any new groups they join. You'll need to experiment with the points for a while to get it right but I think this type of feedback is essential for both the organizers and attendees to weed out undesirable behaviors.