Refund policy is an operations decision

Refund policy is usually written by whoever handles finance and lived with by whoever handles support. The gap between those two is where the last fortnight before an event disappears.

Full refund to a fixed date

The cleanest to explain and the easiest to automate. Everything before the date is self-service; everything after is a transfer. Most of the volume resolves without a person.

Sliding scale

Fair in principle, expensive in practice — every request becomes a calculation and a conversation. If you use one, publish the exact dates and amounts rather than percentages.

Transfer only

The lowest support load and the highest goodwill cost. Works well for free and internal events; poorly for paid public ones.

Whichever you choose, the decisive detail is whether an attendee can act on it themselves at eleven at night without writing to you.