How do i get a bad review removed when the customer was a no show and is responding due to not getting a refund

We have received a very negative review and 1 rating from a customer who was a No Show. Our policy is a 7 day No refund policy and they provided no notice and now are demanding a refund.

Why does booking.com allow them to be able to place a review if they were a No Show. There report effects our rating.