idea: Graph subjective reputation as a service

The idea more-or-less coded in github.com/fiatjaf/multi-service-reputation-rfc, but if it is as good as I think it is, it could be sold for websites without any need for information sharing and without it being an open protocol.

It could be used by websites just to show subjective reputations inside their own site (as that isn't so trivial to build, but it is still desirable).