By issuing most of the hidden city tickets, Korean Air received the bulk of the revenue for doing nothing. Regardless of whether travelers boarded Korean Air flights in Seoul, BA received just $297.50 for flying travelers on Concorde. BA would have no idea if travelers actually boarded in Seoul unless Korean Air volunteered the information, and they didn’t! They lured us in with $875 Concorde fares that cost Korean just $297 and then hammered us later for $7000. That's airlines being airlines....

More hidden city ticketing and fare savings resources:

Korean Air $1.8 million hidden city ticketing claim

The Birth of Hidden City Ticketing Commercialization: ‘Soul for Seoul’ and the $875 Concorde Flight

Travel Agent IDs: How Business Class Was Once Cheaper Than Hidden City Ticketing

Gerald Houlihan Attorney-Defender of the Travel Agent ID (Oh Really?)