@Diana2194 There are 2 different things. If the guests just sends an enquiry, with a question. You just need to reply and answer the question. You do NOT have to approve or decline.
If a guest sends you a booking/reservation request, then you need to accept or decline. If this is the case with your new potential guest, you have 24hrs to do this. I normally reply to their question and if they don't respond, I then contact Airbnb to say they haven't responded and for Airbnb to help out.
If they respond but your are still not happy with the reservation request and If you still want to decline, I would contact Airbnb and ask them to do this for you, explain your reasons clearly and tell them you do not want to be penalised for declining because the guest hasn't replied or because of the bad review you do not want to accept them. Stand your ground on this, politely but firmly. You do not want to decline any booking requests as that then goes against you.
Personally if a potential guest has 1 good review, and 1 very bad review. The red flags would be raised for me. I would probably ask them a few questions about their very bad review. Go on your gut instinct.