@Grigory6 Is this a "Booking Inquiry" or a "Reservation Request"?
You can't "cancel" a request. Cancellation only applies to a confirmed booking. And a request is binding; there's no opportunity to negotiate the price, because when you accept it the guest is automatically charged the listed amount.
If it's only a "Booking Inquiry," you don't have to pre-approve or decline it; the only necessary action is writing a reply. If it's a Request, declining it will not cause your calendar to be blocked.