I didn't think of that. That's true, a decentralised system would make reviews immutable (negative, or positive, fake or real reviews would still persist).
That depends, is there a requirement for the solution to be free?
If you are happy to pay for this, then there are a variety of options with a sliding cost/usefulness/accuracy scale.
If you are looking for reliable, accurate, balanced reviews conducted by anonymous ethical independent agents, and you don’t think consumers of that information should pay for it, then I believe the answer is there is no perfect solution that satisfies all those constraints simultaneously.
If you are happy to pay for this, then there are a variety of options with a sliding cost/usefulness/accuracy scale.
If you are looking for reliable, accurate, balanced reviews conducted by anonymous ethical independent agents, and you don’t think consumers of that information should pay for it, then I believe the answer is there is no perfect solution that satisfies all those constraints simultaneously.