The majority of hotels charge a fee for canceling a room reservation, if one cancels within 24 hours of their scheduled check in. This sort of thing typically isn't an issue if one has a planned vacation or trip, and has ample time to adjust changes in plans. Still, for cancelled or re-routed flights, various emergencies, etc., a Redditor called drwired has come up with a quick solution - reschedule the room for a few days later than it was originally booked, then cancel outside of the 24 hour late fee window.
Theoretically, this tactic should work - hotels mind less if a customer reschedules instead of cancels altogether, and will alter a reservation as long as it stays on the books. Once the date is moved ahead, one can just call back later, and hope to cancel with a different person at the desk. Perhaps it might help to wait a day or two before calling back, as many places keep logs concerning customer issues.
Personally, I have never tried this trick, but I can recall times in the past where it would've been useful. Still, commentary on Reddit concerning the matter kind of makes me think that the tactic doesn't really work very often.