Well we've experienced something likewise with Calam now. We've had to cancel our upcoming event as the registration was low. While we knew some people could not come, there was a big questionmark on people who we believe would register, but just didn't.
It's nice that people tell us that they are coming to our event. It's nice that they say on Facebook that they are going to our event. But we can not take that in account if they do not register on our website and pay the participation fee. Only then are we about 99% sure that those people will really attend.
Now most of the time we don't really make a fuss about this as in 99% of all cases we get the number of expected people in the end. But this time it looked a bit too close a shave for our taste. Certainly with the amount of work it would take us to bring all our gear to the remote location (more than 2hour drive (one way) for us, x2 to get all the gear there). And then all the hours to set up the gear to give our players a nice game location. => look for a 10+ hours to get everything there and set it up.
So we've decided to cancel the event. But we gave a bonus to those who registered on time: they get a free event (excluding food and drinks) and custom scenario. All which will take place in my own forest (yeah, first larp there :-) ). That way those who did register on time and already were preparing themselves for the event will get what they wanted and more. A way of saying 'thank you' from us to them, for registering on time.
So, if you like an event and want the organisers know that you'll attend: register and pay on time!
That way the organisers KNOW that you are really attending.