Hi all,
This just happened to me last week as well. I would agree that it is best to get the guest to make their own account if at all possible. If not, then get contact information for all involved parties.
Let's call our guest Tom. Tom used his brothers brand new account and his mother was paying for it. On check-out day, he came to talk with us about extending the reservation an hour AFTER check-out time. We agreed, but told him "Mom" would need to go online and extend the reservation. He left and was out until after midnight. It didn't happen that day, and we worried for hours that someone else would instant-book and we would have a mess! It was stressful, as we also did not have his phone number.
Biggest problem was not being able to reach anyone. Lesson-always exchange contact information immediately! 2nd problem-realizing airbnb didn't prevent this problem and total strangers can show up on your doorstep. 3rd problem-he didn't know house rules because those were online - parked in wrong spot and didn't know checkout time and was unable to extend reservation himself without relatives interventing.
It would have been helpful to have the mother's contact info too, since she messed up when extending the reservation. She just made a new one and was charged the cleaning fee twice...a mess.
He was a nice guy and it all worked out, but I learned a lesson.
Kristi