The system is a little more nuanced than that because there is a "private review" portion of reviewing where you send a final message to the host specifically about the things they can improve about the space they are renting. The review isn't posted publicly. The host can also send an equivalent review to the guest.

This presents a more honor-based opportunity to leave a review that doesn't risk reputation but still gets a message across. It's honor-based because the host and guests have little pressure to improve from the reviews they receive privately. You don't always need to publicly humiliate people if you have an experience that isn't 100% perfect.