Yes. First, edit your settings to make sure guests who do not have reviews cannot instant book. I normally will not accept a booking request from a guest with no reviews if they are a brand new account, lack profile information, and do not have at least a verified government ID. When I decline a request from someone like that, I will generally list that I'm not comfortable with the guest and enter a comment to the effect that they lack sufficient booking and review history. If they have multiple verified pieces of info, including a government ID, I will consider booking for short stays (1-3 nights) for no reason other than everyone has to make a first booking sometime. Go with your instincts - If a request makes you uncomfortable, don't approve it. Declining an occasional booking should not affect your superhost status, but it will if you decline a lot of requests.