Sample Event Walk/Nav/Etc. on the 31st December 1999

This event is for walking or nav or something… party! and there are 5 slots available; I set the stock on this product to 5. Stock count will go down as people purchase this product. However, if this event does not go ahead.. say you had in the small print that if 3 slots have not been sold by 20th December 1999 users will be refunded, then I’m not sure how this would work. Also, if you took any sort of payment from a user then I’m sure the credit card facilitators would take their commission on the payment regardless and you would then lose that on a refund.