Even though I stay 100+ nights per year at Marriotts and should know what I'm doing, I recently booked inadvertently a nonrefundable rate at the Schaumburg, IL, Renaissance (a very nice, new hotel, by the way). Fortunately, I used the room, so no problem there, but it was amazingly -- and scarily -- easy to book a nonrefundable rate on the Marriott website without even realizing it. I didn't even know it had happened until I saw the charge on my VISA bill!

You might argue for mercy on those grounds -- although I suspect you won't get any.

Bruce