I think ANY platform for reviews is going to get gamed and flooded with fake reviews. I don't see how decentralization would solve that.

A Federated decentralized review platform would have the same issues all current platforms have. The problem is you are asking for authority. From platforms that in general don't require it. It used to be there were a few out there and that you could trust to try to be neutral and nuanced. But so many people in the face of just having money thrown at them find their ethics disposable. And one by one all of them largely fell. If there were an algorithmic or heuristic way to sort the week from the chaff Google Microsoft or someone else would have already done it. They haven't. The only way to really do it would be to curate the reviews. Which would be a lot of work on the part of a lot of people who must already have trust.

But if you manage to crack this problem you will have sold once the biggest issues on the internet.