A to B, costs $300, but A to B to C, costs only $200. You ticket it as A-B-C then walk away at B. Airline loses $100 on the revenue. This is called "Hidden City" ticketing, it is against every airline's rules, but NOT illegal. In US AA or whoever tried to sue, but failed at court as far as I remember. In fact at the time there were writings in the media that airlines pricing policy forced people to use "hidden city" because of airlines gauging.
If you intend to do the "Hidden City" ticketing -
1) do not do it often, once or twice a year is OK.
2) DO NOT use your FF number on the ticketing. Sure you lose some miles but you also save $100. 99.99% of the time, airlines would not go after you. LH's case is because the offender(s) habitually did the "hidden city" ticketing for a very long time, and odaciously put in FF numbers to earn miles. The offender was Very Greedy. Very stupid if you ask me. There was also a guy, also taking advantage of LH, by buying fully refundable intra-Europe business class tickets then feased at LH lounges at air side after security. After that he refunded the ticket in full. Of course he 上得山多終遇虎. 做了 2 年多之後？ LH 發現 將他告上法庭。最後結果如何，我沒有跟進。
For 裏程票 除非該航段已飛出 出票航空公司無需支付該航段的費用。 如果您不乘坐的最後一段恰好 is on 合作夥伴航空公司，那麽出票航空公司實際上可以省錢。我們放棄了許多裏程機票的最後部分，從來沒有任何問題。
唯一的風險是，如果您托運行李 航空公司更改航班，不再在您打算離開的城市中轉。那你就有麻煩了。Because your checked bag will go to the originally ticketed destination!
但以上DL裏程票為例，由於每個人在洛杉磯都必須領取行李過海關，所以這種風險根本不存在!
