Hi Victor,
Indeed, as Branka & Silvia mentioned, if you have Instant Book activated, you can set that only guests with positive reviews from former hosts will be accepted.
If you do not want to do this, you can ask the guests additional questions about them. If they do not respond to your questions, or you are not comfortable with the answers, you may cancel the reservation penalty free so your superhost status will not be affected (Use the reason "I am not comfortable with my guest".). In that case, you better call Airbnb for a second opinion and assistance with the cancellation.