@Mvp0 I have accepted plenty of guests with only a phone number and email and they all ended up being charming guests. I look at their profile write-up, and their past reviews first (some guests don't have any) and then I communicate with them. You can tell a lot from the way someone communicates as to what kind of guest they will be, although it's not foolproof. Thank the guest for their interest in your place, ask any questions you have, make sure they have throroughly read all your listing info, reiterate any important points you need them to be aware of.
If it is an Inquiry, you don't need to decline those- just messaging back within 24 hours is all that's required. If you feel okay about the guest after messaging with them, go ahead and pre-approve the Inquiry.
If it's a Booking Request (different from an Inquiry) you do need to either Accept or Decline within 24 hours, but you can still message with the guest before the clock runs out.
Continuing to decline inquiries and requests will result in Airbnb sending you warning messages and possibly closing your listing. It also affects your Acceptance rate, which if it falls below the target %, will lead to delisting.
I suggest you use the search engine here to find posts on "Red Flags" which will lead you to threads alerting you to what to watch out for in your vetting procedures.