I have my doubts about karma / kudos / credits or something similar. These things works pretty well online on fora because there is high visibly and high activity. Having a bad karma really impacts your day to day activities.
I think that it will hardly have any effect on motivating people to actually show up at momo. The benefit of a high karma is also minimal. It might even have the opposite effect in the long run. People with high karma might use those points to not show up as it won’t impact them that much. It’s just like the climate change issue. People don’t feel the need to change because the impact is too low on their day to day life.

We’ll probably conclude in the end that there is no perfect solution but thats not what we’re looking for. We’re looking for the most honest one.

1) show a list of the persons who RSVP’d on the site, but didn’t show up. But I guess a Wall of Shame is a REALLY bad idea with a lot implications like google indexing those pages and that page turning up as #1 position for their name…. that punishment is a bit harsch.

2) a remix of Joost’s #2: “Don’t allow entry to people who didn’t show the last time around.”…
Automatically “bench” the persons who’ve RSVP’d, didn’t come and didn’t free their seat the last time. “Bench” as in: if someone frees his/her spot, the a benched person receives a seat. This way they’re in the same spot as countless others the previous time. Let’s call this the “what comes around, comes around” solution.

3) Give people “karma points”, and the “karma points” * “first come first serve” determines who gets the seats. For example: I’ve been to 9 out of 10 Momo’s and never bailed out. So that will give me –as a regular Momo attendee– high Karma. On the other hand: people who signed up but didn’t attend will get negative Karma points, so they’ll have to sign up REALLY fast to get a seat. If they DO get a seat but don’t turn up, their karma points go even more down.
Key to this solution is that high Karma people can’t get a too high karma score. Else new people to Momo don’t have the opportunity to ever attend.

(but then again, they will make an alias in the meetup…)

I agree also with Dirkjan: everybody gets greedy when weeks in advance you get notified that there are to less tickets and you must react within minutes.

Make a lottery? Oldest Meetup members receive more lotery tickets. Like I will receive a ticket for every momo attended. (thats 11 tickets…)

Making people pay in advance (and then returning that e.g. by getting them two free beverages) is also going to work, but yeah…

C’est le ton qui fait la musique.

2. Don’t allow entry to people who didn’t show the last time around. Disadvantages: Might give a bad feeling, feels somewhat ‘childish’ to punish them.

No perfect solutions, but maybe it’ll help.