Hi @S1,
You are not obligated to provide a refund but it might be a nice gesture to your guest if you can be certain that guest is not staying anymore than three nights. I do not know the situation but unfortunately for the guest, there is no way to book 3 guests for 8 nights and 1 guest for three nights. I would probably provide a refund for the five nights as I would look at it as the guest being honest by booking the right number. Many others might have only booked for 3 guests and just snuck the fourth guest in.
I would also think about the review you may get for not refunding for the guest who is only staying 3 nights as opposed to the review you will get for providing a refund for those days not stayed.
Dave
David
Superhost Ambassador ~ Host Club Community Leader ~ Experienced Co-Host