It is difficult to comment given you have not specified what the item was. It would definitely become a dispute between you & the guest, Airbnb won't make a decision without contacting the guest first. You have to make a claim right away, should have been immediate but for sure within 48 hours of guest's departure. Sometimes it is difficult to prove the guest was responsible for damage unless he admits fault. Even then, you need it in writing. You will have to decide which is more important, the money or the good review. Maybe it would be best to replace the item with something less breakable, or to not replace it for guest use. Of course you are entitled to replacement cost, but maybe in future just keep it for personal use. Remember that you can explain the reasons for their bad review beneath it, so if you have lots of positive reviews, it shouldn't make a huge impact. Reasonable people will understand that you were entitled to replacement cost.