@Lucinda26, if the guest is merely sending an Inquiry (as opposed to a Reservation Request), all you have to do to fulfill your obligation as a host is to send a message back in reply. You do NOT have to Decline it.
So to be clear, if your button options are "Pre-Approve" or "Decline", it is just an Inquiry, and all you have to do is send back a message. You do not have to push either the "Pre-Approve" or "Decline" button.
For every single Inquiry I have ever received, I have always just responded with a message and have never once had to push the "Decline" button. My response rate is 100%.
I also contacted AirBnB host support and asked them to verify this is true, and they said yes. All you have to do is send back a message.