Yes. Once someone has checked in they can’t be removed. If they insist on overselling their flights then they need to refund twofold those that can’t take the flight. First for not being able to take the flight and second for the inconvenience and a penalty for their greediness of putting profits before paying customers. To get out of the penalty part they can put them on the next flight going to their destination, even if that means another airline, at the airline’s cost. No matter what the customer is fully refunded.