@Laura5023 I'm not sure what you don't understand. Guests are notified when they try to book a listing for the same dates that they already have an active booking for that they won't get their service fees back, as per the wording you quoted. If they ignore that, that's their problem.
The only thing to tell the guest is that hosts gave nothing to do with Airbnb service fees and policies, that's something they have to contact Airbnb about.
This policy is designed to prevent guests from shopping around, booking more than one place to "hold" it, blocking up the host' calendars, then cancelling all but one.