I agree, it’s a very common problem for free events, Nick. It’s such a shame when there is a waitlist, and the organisers have gone to so much trouble, and sponsors have given hard earned cash. I had to travel to Brazil at short notice recently, and therefore couldn’t make it to UKGovhack, but did remember to send apologies beforehand. With Open Data Camp and BlueLightCamp we always have no-shows. When allocating tickets and catering we assume a 25% dropout rate based on previous experience (probably a bit higher than that on the Sunday of a 2 day weekend event). What to do? Perhaps consider a small, refundable, deposit?