Originally Posted by LchChester

Bidding can capture the consumer's surplus, by selling the remaining unsold seats to those value them less then the lowest fare available.

The trade-off for CX is that people who are elastic may choose to fly one lower cabin and bid for the unsold seat instead - even worse people who are flexible with their travel time (like my grandparents who are retired), may buy a rebook-able fare bidding for the upgrade and board only when their upgrade bid is cleared, assuming that the bidding system does not clear as late as when boarding.