@Monika64 I just wanted to give you an update on this subject. Since it really bothered me that I did not know that the search function worked this way, I decided to consult with some Airbnb wizards and have more information for you.
Keep in mind that the search function considers all users as guests when searching. The system has no way of knowing when a host is looking for their own listing or that they are a host.
1. When a host has set their IB settings to require previous positive reviews, only guests that qualify will see all the IB listings that otherwise match their preferences (filters) such as location, number of guests, amenities, etc. Guests (and hosts) who do not yet have positive reviews will not see these listings in their search results because they are ineligible to book. The system will know if they are eligible or not only if they are logged in. If a guest is not logged in, the system can't see if they qualify and will assume they do not.
2. A search with the IB filter "On" will display IB listings with the positive reviews requirement to all guest who have them.
Those guests who do not yet have positive reviews will see only see IB listings where the host has not set the requirement for positive reviews.
3. A guest (or host) that does not yet have positive reviews and have set the IB filter search to "off" will see all listings available that match their preference. An IB listing which has the "positive reviews" requirement set will not appear as an IB listing and guest will not be able to Instant Book. A guest without positive reviews can still book this listing, but it will be processed as a Reservation Request where the host can check out the guest and decide whether to host the guest or not. Just like a non-IB listing. This is why you may receive a Reservation Request instead of an Instant Booking.
So essentially it works like this with searches with the IB filter "on":
Guest with previous positive reviews = sees all IB listings
Guest not logged in or guest without positive reviews = IB listings that do not have the previous positive review set.
Searches the IB filter "off":
Guests with positive reviews = all listings including all IB listings
Guests without positive reviews or not logged in = all listings including IB without the positive review requirement and IB listings with the requirement but they will appear as non-IB listings (guest will need to send Reservation Request).
Clear as mud? Feel free to ask me questions so I can clarify!
Clare