What change are you expecting to see exactly?
I really don’t understand how/why some people automatically assume that just because a seller has a lot of positive reviews, these reviews are fraudulent.
To leave a review, a buyer has to buy a service. This means that a seller attempting to play the system needs to set up another account and spend money buying from themselves. MAYBE a determined seller could be stupid enough to invest $100 in this kind of activity. Still, though, real reviews from real buyers are not going to be all glowing 5-stars if a seller can’t deliver on what they say they can in the long-term.
As a buyer myself, I have never had a problem assessing sellers by their ratings. Usually, buyers who regularly experience poor quality of service on Fiverr are simply not using a reasonable level of due diligence to vet sellers.
It is already against Fiverr TOS for sellers to ask for reviews. If a seller does this, a buyer can report them and their account will be banned. In like regard, if a seller has multiple reviews from a client which obviously look fake, they too can be reported.
What exactly is the solution you want to see implemented here?