I admit I HATE Instant Booking and I believe it makes more harm than good but I was forced to turned it on as Airbnb is very clear about that if you don’t have it you will not be visible for the people browsing the site.
I have turned on IB just 2 weeks ago and I’m surprised how quickly problems have arrived. I have recently received an IB for a girl that booked my place for her parents. So the reservation was made for a third party which is disallowed by Airbnb as it is stated in the following FAQ.
I have received many inquiries for third party bookings in the past but I was able to decline them without IB. This is a clear example of why IB sucks!