Can guests who choose not to stay leave a review?

[Salem2]

Recently I had a couple book to stay at one of my rooms.

On arrival they decided they did not like the listing and did not want to stay, I have a strict cancellation policy but since they were not happy and did not use the room I thought it only fair to refund them the money. I did not realise at the time (because its the first time this has happened to me) but they did not actually cancel their reservation, they simply requested a refund. Now they have left what is surely a negative review which seems unfair since they did not stay at the listing!

What is airbnb policy? if a guest cancels, can they still write a review?

These people run their own Airbnb listing and have more experience than I do, now I feel I have been tricked. I refunded the money and they thanked me by writing a nasty review. I really struggle to do the best that I can and now I am very saddened and discouraged.