If you check the terms and conditions on the frequent travel credits, it states that they are not transferable(see below)
Certificate Terms and Conditions
Redeeming your certificates
When booking your next trip with Grand Circle Travel or Overseas Adventure Travel, simply ask your Travel Counselor to apply your credits to your new reservations. All credits must be issued in your name. Credits are not applicable toward initial deposit and are not transferable. Expiration dates cannot be extended.
Frequent Traveler Certificates
- This certificate is not applicable toward initial deposit.
- This certificate is non-transferable.