Non-refundable clauses are 100% up to the host. It is incumbent upon the person who books a place to see what the policy is when it is booked.

For example, at the moment, I have a three-night booking that is to begin on 29 April. This is what the policy is for this place, as I just looked it up:

Cancellation policy

Cancel by

Cancel by April 27 at 3:00 PM and you'll get a Full refund: Get back 100% of what you paid..

Apr 27

3:00 PM

Full refund: Get back 100% of what you paid.

Cancel by April 29 at 10:00 AM and you'll get a No refund.

Apr 29

10:00 AM

(check-out)

No refund

So, as you can see, if I were to find myself in the same situation as Carly, I would have no adverse financial repercussions for canceling now.