@Melanie58 Yes this is one of the perks for hosts who choose to have Instant Book enabled and who have chosen that guests have positive reviews from hosts in order to book instantly. Those hosts whose listing do not have Instant Book enabled do not have this feature.
Be aware, however, that any guest that does not meet your requirement will still be able to send inquiries and / or reservation requests where you will need to decide whether to accept or not.
This requirement for Instant Book hosts is a real bonus and alleviates many of the fears hosts have about using Instant Book.
Cheers!
Clare