Hi @MaryAnn22 you do not have to "pre-approve" or "decline" guests during the inquiry stage. I almost never pre-approve guests, and I almost never decline a request. I simply reply to them to keep my response rate up, and then do nothing. What DOES affect your standing, and what you must not do too often, is decline a Booking or Reservation Request, as in someone is ready to commit to the booking, and ready to pay.
I personally do not flag guests simply for being unfamiliar with the Airbnb process and wanting to make private arrangements such as paying outside of the platform, etc. I just tell them - bookings on this platform are processed on this platform.
I am a bit different maybe. Clients that come to me directly through referrals, repeat bookings, my own marketing initiatives, etc I am very happy to make private reservations with, and process their payment directly. I do not want to have all of my business tied up with any one platform. But a guest that comes to me on Airbnb stays on Airbnb, and a guest that comes to me off Airbnb stay off Airbnb.