The website is designed in a quite non-intuitive way and requires some experience from users, to be navigated easily, so I guess half of the blame is on ABB, half on guests. Putting 'Reserve' and 'Contact host' next to each other should do the job.
However, this whole thing wouldn't even be that big of a problem if guests would keep the persistent flow of communication and respond to our, sometimes, immediate responses in a somewhat timely manner, until the issue is solved or agreement reached.
Instead, they throw a question, you respond to them within less than a minute, asking for some clarification or adjustment, and the next message from the guy/gal comes after six or so hours, if at all. In the meantime, your calendar is blocked and your response rate lowered with every passing hour.
The real kicker is that about half of these requests, we do not accept for their own good; we know right away from their message that they have no clue what they are booking, i.e. they didn't read even basic info about our place and location.