There's a problem I have seen at a number of free events, particularly "unconference" events which have a limited capacity. There will be a sign-up list, and once it fills up, people are turned away or get on a waiting list. (Some online ticket services now support the idea of free tickets for this purpose.)

Then you get to the event and 1/3 of the seats are empty. Because it did not cost anything to sign up, people were quite willing to no-show, and many other people signed up "just in case." Unfortunately many who would have come decided not to go because the event was full.

To counter this, many events have started putting on a small charge "just for the sake of having a charge." This charge is in the range of $10 to $30. It discourages signing up just in case, and makes people feel a little more strongly that they should come, but it's not a burden for most people and raises a small amount of money for the event. (Usually such events are really paid for by sponsors or donors.)

Here's another idea: Set a price for the event and take and authorize a credit card, but only charge the credit cards of the no-shows. This requires some sort of on-site desk where people can register to not get charged (or get a refund if they used another mechanism like paypal, cheuque or cash.)

The big question is, what should the price be? Many factors change as you change the price:

• If the price is very high, you start scaring people away from registering, but you will get very few no-shows.
• If the price is very low, you may still get plenty of no-shows, but now there is at least revenue for it ... and empty seats.
• For some price ranges, a large fraction of the crowd may elect not to refund even though they are at the event, either because it's a hassle, or they feel like donating. They may feel themselves as cheap by going to ask for their $30 back from a non-profit ad-hoc event. This can help pay for the event.

While it will vary based on the type of event and wealth of the crowd, there is probably an optimal price, which can only be found by experimentation, that both comes as close as possible to filling the room and generating the most revenue from no-shows. It is not out of the question that there could be a price which (combined with a subtle pressure on people to donate rather than refund) pays for the conference.

People who plan to no-show could cancel before the event, possibly just a day before if there is a waiting list. People on the waiting list would not have to pay, but could be told on the morning of the event if they are in. A well managed, real-time waiting list with good predictions on whether people will make it can help assure the room is full.

People who are spending other money to get the conference (ie. booking a flight or hotel) might not have to pay, as they have other penalties for not showing. It's mostly locals who do the "just in case" sign-up.

If anybody tries this, I would be interested in getting reports about the price and how people reacted to it and how many refunded. Slightly harder is figuring out how many people are scared away by the price, even with the refund promise. Events that are free tend to be free for a reason, and this system might not meet those goals.

Logistics

It would also be nice if ticket services supported this model. It makes sense, as they would get a small cut of any ticket not refunded. Refunds to paypal tend to cost you nothing, though I could see those services getting upset at merchants who are refunding almost all purchases and just using them as a vehicle for free. With cheques, one can also simply not deposit the cheque and even hand it back to the attendee at the conference. But since credit cards and paypal make it so easy, it is tempting to insist on those, and just allow a small fraction of the people to plead that they have no accounts, warning them the exceptions are personally reviewed.

You want to be able to process refunds without a large cost of volunteer or staff time. Of course if there is a registration desk you know who showed up and who didn't, but most free events don't want to have such a desk. If everybody uses a credit card, a number of options exist for a self-service desk. For example, they could just swipe the credit card they used at a self-swipe station, as counter-intuitive as "swipe to not be charged" might be. A station which photographs a person's card or ID could also be self-serve, but requires post-processing.

The web page could also offer a QR code to print, and that printout could be brought and scanned to assure the refund. This could be done by a volunteer's smartphone, or a self service station with PC and webcam. They need not actually print the code, as cameras can read a QR code from the attendee's phone screen. Printouts though can also do a pre-printed attendee badge, allowing the person to just cut that out and pick up a badge-holder for it.

This does allow a small amount of cheating, where a no-show asks a friend to print out and show their refund page, but if the fee is low, I doubt there will be much of this. If there is already a staff desk, as most events have, placing the self-serve refund scanner there will discourage people from using it twice just to save a friend some money.

Note that having a refund desk where people have to come in person to ask for their refund will mean that more people decide to donate, so depending on the goals of the event, it may make sense to deliberately not make it trivial to get the refund. Some sponsored events may truly not wish the money, some may be secretly happy for it.

You do want to be sure you are accurate, so that people don't complain they never got a refund after the fact. Again, I think cheating will be low in this area so it may not be a big concern.

Then, at the end of the conference, send an email to all on their refund status. This allows protests from those who thought they refunded. If the scanner is on-line, it could have emailed about the scan right then and there, and many can see that email right away. For a small amount of money you can also send a text message confirmation; just about anybody can get that.