Hidden city travel is a great way to save money on certain overpriced flights, but it does come with several risks. If your intended destination is a hub city, you could book a flight to a fake destination and end your trip midway when you connect at your intended destination.
A great example of this is St. Louis to Charlotte. American prices this flight extremely high at $534 one-way to capture revenue from business travelers who only book direct flights. Luckily, the website Skiplagged.com (my referral; $10 free credit) allows you to easily find hidden city routes. Here, American prices the same exact flight from St. Louis to Charlotte, but continuing on to Cancun for only $165, since that is a leisure traveler route instead of a business traveler route.
Hubs- Hidden City works great going to an airline's hub, but it does not work as well in reverse. In the example below, American only flies to St. Louis from seven cities. Whereas, American flies to about one hundred different destinations from their Charlotte hub. With more destinations, it is more likely that one or two of those destinations from Charlotte's airport will be very cheap.
Regular Flight at $534
Same Flight With Cancun As Destination for $165
I have flown via Hidden City Travel many times without issues, but you need to be aware of the requirements and risk.
One Way Flights Only- You can only book one-way flights. If you book a round-trip flight and miss any segment, the airline will automatically cancel your remaining ticket.
No Checked Bags- You cannot check a bag. If you do, your bag will end up at your final destination, which is not where you are going. Also, do not let them gate check your carry on bag to your final destination. Tagging the bag and picking it up in the jetway is fine. This issue will mostly arise if you are flying on a small regional jet or in the last boarding group.
Points- Some people associate their frequent flyer number when they book a hidden city route. If I have a large number of points in my account, I will create another airline account, and use that account if I am doing a hidden city routing. This allows me to still get points for the flight and avoids risking my large points balance if I piss off the airline. United Airlines sent out letters to travelers who did about 50+ hidden city tickets since they were earning points and elite status through hidden city travel.
Flight Changes- Occasionally a flight will get canceled or changed. If your flight gets canceled, you would need them to book a similar routing through the city you wanted to visit. If your flight schedule changes at the last minute, you could be out of luck. I had this issue one time when I booked O'Hare- STL (exit point)- NYC. There was a last minute schedule change, and for some reason, United changed the routing to O'Hare-STL-O'Hare-NYC, which luckily allowed me to get off in St. Louis as planned.
Passport- In my example above, I booked a flight to Cancun. You will need a passport to check in for that route, despite not flying the international segment. Therefore, be sure your passport is valid and with you if you book an international flight.