The short answer is yes. The long answer is yes, you can cancel instant bookings penalty-free if you have valid reasons for doing so that does not violate Airbnb’s non-discriminatory policy. These reasons can include causes that led you to believe that the guest is unreliable. Also, in case the guest keeps ditching your mails and avoids replying to you, or in their reply, they mention that they are going to break your house rules by bringing in a pet (when your house rules forbid this), then based on such reasons you can terminate their booking penalty-free.