Hey. I'm very interested in finding a solution for this problem as well. I think there's value in decentralized review system. Also with regards to reputation, i'm thinking one could also pull in reputation from existing social networks such as twitter, linkedin, bitcointalk. i.e if a review is coming from someone like vitalik for example, it adds more weight compared to others. And something like keybase can already be leveraged to prove identity. With regards to "set standards", i'm not sure if there should be one at all, but a simple 'steam like review' system could work i think with some added UI that highlights and groups reviews into summaries of common points so that people can get a better picture of what other's think.

I'm a developer, have done some blockchain related projects, and would love to discuss this more.