@Nicole2592 This might not be the answer you want to hear, but you have yourself mostly to blame on this one.
First, if everything you said around the circumstances of this guest interaction is true, you had exactly zero reason to refund them. Not a single penny, let alone a full refund and helping them find a new place? Outrageous.
76 degrees in the shelter of a home would feel like a refrigerator when coming from 104 in the sun outside. 28 degrees cooler is 28 degrees cooler. The guest clearly had other issues and they tried to say the supposed "bad A/C" was the problem. It's nonsense. They steamrolled you. Next time, you apologize, you ask for them to graciously give you their patience (I mean, it's 104 out, that's fricken hot), and you never give money away. We are not in business of donating money to others. Once they pay, and you give them a fine accommodation (which you did), the moment you give money back to them, it's a donation. Plain and simple.
Next, you knew they he had the ability to leave a review. Crunch time was way back once the guest had already checked in. So knowing they could leave the review, it begs the question even more: why surrender the money? That risk was always there and you kinda let it happen to you.
Now, I'm not saying the Airbnb ranking system is perfect. Far from it. And if a guest doesn't stay at a house, they should NOT be able to review you! But that's not how it works right now. And so you need to protect your business based on the rules that are in place at THIS moment. You didn't do the best job of that and sadly you got punished for it.
Let this NEVER happen again. For yourself, and for other hosts!
And, in general, don't give money away! Just don't do it! Makes it harder on everyone when these jerks stay at other listings and expect "refunds" for whatever they think the are entitled do.