I booked a flight back from Hawaii with airmiles but during check out, I picked the wrong airport for arrival (it was a layover so the same plane was the "start time" for two different places). i realized it no less than 2 min after I got the confirmation so I called to see if i could change it, they said no, they could cancel my flight back but would charge me some crazy amount of miles then I could rebook it (but I would be about 500 miles short when i rebooked it). I was like "this was LESS Than 5 min ago, are you serious?" I ended up tweeting about it and the airline hit me with the "we will do it but just this once." so yeah, now i'm super careful but I feel like if it's the same day, they should allow a pass.