Instant booking allows you to decline if you can provide a good reason.
I've yet to decline anyone on Instant Booking but my understanding is that if you decide to decline, you can check off a box that says you're not comfortable with the person.
I don't know if you'll be required to explain why the discomfort, but others who have gone through the process may be more helpful.
Plenty of people have an issue with IB and others don't. I think different parts of the world are better suited to vetting thoroughly before accepting a reservation, but I live in Snoozeville and our idea of excitement is when Mrs. Hermann's cat gets out and starts attacking the dogs in the hood.