Reviewing a guest is an important element of the Airbnb ecosystem.
"Hosts are encouraged to send a review for the guest as this increases the probability of the guest writing one for the Host and the listing. The Host can provide category ratings, offer private and public feedback as well as indicate to recommend the guest to other Hosts."
To leave a review for an Airbnb guest, open the guest control panel for the guest and navigate to the Correspondence tab. There you will see a button for "Create Guest Review".
Once clicked, a window will open to submit a guest review for an Airbnb guest:
to learn more, please visit the Airbnb Resource Center: