14 CFR 380.15: Substitution for charter participants.

Substitutes may be arranged for charter participants at any time preceding departure. Participants who provide the charter operator or its sales agent with a substitute participant, or who are substituted for by a participant found by the operator, shall receive a refund of all moneys paid to the operator, except that the operator may reserve the right to retain an administrative fee not to exceed $25 for effecting the substitution.