Unfortunately, my only recourse for a bad experience "out the gate" is to leave a bad review here.
I made a reservation several days in advance - clicked book, and immediately realized that I had accidentally entered an extra day than I meant to. I wrote to ex pedia to try to correct the situation within 5 minutes of making the mistake, and they reached out to the property on my behalf. They could not refund or all me to cancel.
I tried calling the property myself, thinking that if I spoke to another human, they might understand the mistake better. The woman I spoke with was very kind and sympathetic, but told me there was nothing to do, and that I had to p ay for the extra night. Definitely disappointing, for all parties, I'm sure.