Not sure what to say about a bad review. Maybe push for some good reviews/recommendations from friends and such to try and compensate?
I just had a dog this weekend that peed in my house 7 times, so I feel your pain. Did you have a meet and greet before you approved the booking? If not, I would strongly suggest trying that next time, although admittedly it's not a perfect solution. For me it's just a way to look for red flags but I've certainly not seen them all )^:
This person sounds unreasonable and it seems like they did not do a good job of informing you of the dog's situation. Good luck with the next people, I think the "bad" dog owners are less common.