@Michael5736 As you are accustomed to IB bookings, make sure you understand the difference between an inquiry and a request.
For inquiries, you only have to answer their message within 24 hrs, you don't have to click on pre-approve or decline.
For requests, you do have to either accept or decline within 24 hrs, and declining affects your Acceptance rate. So one tactic is to encourage the guest to withdraw the request if you woukdn't accept it. Briefly explain to the guest why you can't accept, and make it sound like it is to their advantage to withdraw the request, so they will be free to place another request for a listing that meets their needs. If they withdraw it before the 24 hrs is up, you won't have to decline.
As a host who has never used IB, I can tell you that I have accepted guests with no reviews and they have been fine guests. Vetting on your own requires a combo of checking out their past reviews, if they have any, looking at their profile write-up, if they have bothered to fill it out, and how they communicate with you.
If they respond in a timely fashion, are articulate and polite, give you some info about themselves, or why they are coming to the area, and answer any questions you pose to them, those are all signs that they will be good guests.
If they are new to Airbnb, you should make sure they have thoroughly read through your listing info and house rules, are aware of your cancellation policy, etc. and understand that only guests accounted for on the booking will be admitted to the property.
For sure it takes more time than IB, but I can tell you that I have never had a bad guest even though they wouldn't have met IB criteria.