With skiplagging, people typically purchase the outgoing journey on one airline and the return on a different airline (or at least a different itinerary) to avoid being caught. Thus, there wouldn't/shouldn't be a need to change airlines in one journey.
For the CLE-DTW-LAX hypothetical, if a person wants to go from Cleveland to Detroit but notices that a one-way to LAX through Detroit is cheaper, they'd buy the one-way from Cleveland to L.A. through Detroit, but only fly the CLE-DTW leg of the itinerary. OTOH, if that person wanted to go to L.A. from Cleveland and found that the trip is cheaper if you cobble together one ticket from CLE-DTW and another from DTW-LAX, then that is
not considered skiplagging and is not against the rules.
There were/are a few apps that specialize in finding cheaper airfares using the skiplag trick. They've all been sued by the major airlines but have survived. There are a few things to keep in mind for it to be successful:
- Do not check bags.
- Do not connect the itinerary to a frequent flyer account or use an airline credit card. This will make it easy for the airline to figure out what you've done.
- Do not try attempt to do with a round trip ticket. If you buy a r/t from CLE-DTW-LAX and expect to just take the CLE-DTW legs back and forth, you'll get stranded. The airline will cancel the entire ticket after you miss the second leg of the trip from DTW-LAX.