14 C.F.R. § 381.9 – Sales.

(a) Except as provided in paragraph (b) of this section:
1. (1) No operator of a Special Event Tour shall accept money for a seat on a Special Event Tour, or authorize an agent to accept such money, unless the operator has physical possession of, or written contracts (in the manner described in § 381.7) for, a ticket for admission to the event for that individual. To the extent that the operator receives an unsolicited booking for which the operator does not have physical possession of or written contracts for a ticket for admission to the event, any payment accompanying that booking must be returned within 3 business days.
2. (2) Upon acceptance of the money for a sale, the operator must reserve one event ticket for that individual. An operator may not sell more seats on the tour than it has event tickets in hand or under contract. (An operator need not continue to reserve an event ticket for an individual who withdraws from the tour by providing notice to the operator or by being notified by the operator that the individual's participation has been canceled due to failure to remit a required installment payment.)
(b) An operator of a Special Event Tour may accept a booking and payment from an individual for whom the operator does not have an event ticket in hand or under contract if that individual agrees in writing that he or she understands that no event ticket has been reserved for him or her. This agreement shall specify whether the person has agreed to participate in the tour without an event ticket and/or the operator has agreed to attempt to acquire an event ticket for this person. If the two parties agree that the operator will attempt to acquire an event ticket, the agreement shall specify any penalties that will apply if the individual later cancels because an event ticket did not become available. If the operator notifies this person that an event ticket has become available, that person shall enjoy all the other protections of this part from that time.