Originally Posted by
MSPeconomist
Regardless whom you call, keep a record of names (with titles, phone numbers and email addresses if they're hotel personnel) and times of the call. Try to get a follow-up email if possible or a cancellation confirmation with a time stamp as close as possible to the time the reservation was erroneously made. Better documentation will make it easier if there's a mistake and you're charged for the night/deposit/stay.
Good advice.
The system generated confirmation email and cancellation emailed showed the exact same timestamp (same minute) since I literally pressed cancel right after I accidentally booked the reservation. I am assuming the Marriott CS and the hotel could see what time the reservation was created and cancelled, but if they didn't I knew I at least had the system emails to try to help my case (even though it's my own mistake...).