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 上得山多终遇虎. 做了 2 年多之后？ LH 发现 将他告上法庭。最后结果如何，我没有跟进。
For 里程票 除非该航段已飞出 出票航空公司无需支付该航段的费用。 如果您不乘坐的最后一段恰好 is on 合作伙伴航空公司，那么出票航空公司实际上可以省钱。我们放弃了许多里程机票的最后部分，从来没有任何问题。
唯一的风险是，如果您托运行李 航空公司更改航班，不再在您打算离开的城市中转。那你就有麻烦了。Because your checked bag will go to the originally ticketed destination!
但以上DL里程票为例，由于每个人在洛杉矶都必须领取行李过海关，所以这种风险根本不存在!
