The moment you have community rankings on search, and your search gets popular, you land in a war zone with bots trying to mangle those. Reddit is kind of good dealing with that, but it is very resource intensive.
I'm sure you could still manage to make "fake" accounts but it would be much more difficult, and linking them together would be much easier.
Of course starting a site like this would be very difficult. But maybe you could start without it then add it in once you get to a decent popularity such that many people can find a referral if they need to.
In China, all social accounts must be associated with a phone number, and phone numbers are tied to government identities. It doesn't stop any manipulation of scores and rankings.
> then keep track of their credibility?
It is very likely China will do that too soon. I think you can already imagine the ramifications.
However it could just be reputation based like on Wikipedia
source: worked in ads and search for decades, incl google.