Hi @Thomas407
I really hope that you have their conversation about the issues, and the promise of a good review in return of a refund in writing.
If so, make the 1st step : contact airbnb and alert THEM about the guest and their plot. Make sure they are aware - if the guest goes ahead, you may even be able to get the review removed (rare, but happens).
Also, add, in writing, that you spoke to then on they XX (2 days after their check in) and they had no complaints at that point.
in the terms, it says that guests need to flag issues to hosts and give them reasonable time to fix them. You can also tell them that.