As a guest, I have recommended on several occasions to AirBnB that rental agreements be made available with the listing (not something to be requested by messaging a host).
At a minimum, it would be helpful to filter listings based upon whether additional rental agreements will be needed. This seems like an incredible easy fix.
As stated by others, it is unfair to ask guests to agree to different, sometimes conflicting, contractual terms after booking. It is also frustrating to be surprised by additional demands for completing a reservations after booking.
These surprises diminish the fidelity of the information on AirBnB, which is central to the service it provides.