It helps to observe how symmetrical something is, to understand how equitable it is. In this case, if you want more seats, they'll happily give them to you and

It helps to observe how symmetrical something is, to understand how equitable it is. In this case, if you want more seats, they'll happily give them to you and charge more, so it would seem fair that they should also be happy to reduce the number of seats and charge you less or refund you. If they only accept increases and not decreases, it's not particularly equitable.