@Monica4 It might be the case that AirBnB *is* using different default settings (IB on/off as a search filter) for different searchers or even for different geographic locations. However, in my case, it is always Off by default. This is true regardless of browser, regardless of computer, and even in the iPhone app. I can even set it to ON, run a search, and then clear my browser's search history and all cookies, close the browser, then restart it, and IB as a search filter again defaults to OFF.
I also want to say again that my particular listing, which does NOT use IB, is always quite high in search results (using a cookie-free and history free-browser when not logged in, in order to replicate random guest searches). In fact, it's occasionally even in the #1 position for the entire Austin area (over a million people, and zillions of AirBnB listings). and even more often if the search is limited to our zipcode (which happens to be one of the more desireable in Austin for travelers, and contains several hundred AirBnB listings). My point there isn't to show off, but to suggest that even if AirBnB does sometimes place non-IB listings slightly lower in the search results, the effect is either very, very small, or can be overcome by other factors. Such as consistently high ratings, consistent high booking levels (makes AirBnB more money), consistently prompt host responses, high request acceptance level, low or non-existent cancellations, and so on.
Many times when a host asks for help because they're not getting as many bookings or inquiries as they used to or think they should, I find that if I go look at their listing, they have either weak descriptions, massively over-long or poorly composed descriptions, or a poorly-checked set of amenities. The latter can get a listing filtered out from the git-go. For example, people who don't check off the box for "Hangers" -- how hard is that to remedy? Or people who check off WiFi but don't check off Internet. Or people who don't check off "Laptop friendly workspace" when their photos clearly show a table and a chair. Or don't supply an iron, or a hair dryer, and so on.