My friend, who is 1k was flying stand by ORD-DEN. He first received departure management card and then at the gate Boarding pass. When he boarded the flight he found his seat occupied by another person. Both BPs had the same seat #. Some supervisor came on board and asked him to go on the next flight, since there are absolutely no seats left. When he finally arrived DEN he approached Customer Service, but was denied any compensation, since the flight he bought departed many hours ago. Any idea if this is IDB and should he keep pushing?