That’s tough since there’s rarely a penalty for registering or skipping. Both are easy to do (or not). Incentives guide behavior and “free” messes them up.
There's no such thing as a free event. Even if attendees don't pay with money, they pay with time. Since time is precious, not going is cheaper.
Here are four ways to deal with no-shows.
The “Will You” StrategyThe fourth universal principle of influence is Consistency. We tend to behave in ways that match what we did in the past, especially when others can see us.
A restaurant reduced no-shows from 30% to 10% by adding two words to their confirmations. When making reservations, guests were asked “Will you please call if you have to change or cancel your reservation?”
Your registration form could have an extra question: “Will you please email if you are unable to attend?”
Your event reminder emails can have a similar message. Isn’t this making cancellation too easy? Perhaps, but you’ll get a better sense of how many are attending. That’s valuable too. By encouraging cancellations, you’re implying there’s demand for the seats. Scarcity is another universal principal of influence.
The Public CommitmentWe’re more likely to do what we say in public. Eventbrite lets your Facebook contacts know that you're attending. Meetup does too. Others may even attend because of you. Now cancelling is tougher.
Eventbrite lets organizers show the names of the registrants. That may also help get more registrations and higher attendance.
Refundable DepositsSince people are loss averse, you can use the power of money as an incentive. Although your event is free, you can charge a deposit to reserve a (general admission) seat and give a refund to those who show up. The no-shows are then the only ones who pay. That seems fair.
The penalties may not be enough to cover the costs for refreshments. You could ask attendees if they would like to donate their deposit to help fund the event. That gives attendees an opportunity to help if they are willing and able. As an extension, you could ask for donations to get money from people who support the cause but can't participate.
“… it is our policy to overbook. In case of a full program, your reservation may not guarantee admission. Unclaimed reservations will be released to standby customers ten minutes prior to the start of the program. We recommend that you arrive early.” --- Toronto Public Library Appel SalonAs you hold similar events, you'll get a sense of how many people don't show up. You can then overbook and encourage people show up early to save their spot. For a popular event, you may have to turn people away. The rejected ones won’t be happy, but they have an incentive to arrive earlier in the future.