In any distributed trust system you can really only calculate based on volume and value and both of those things are easily manipulated since there is no way to identify individuals.

Also you have the situation with your nodes of then requiring an additional layer of trust on the network to determine which nodes are to be trusted.

You can't even do things like lower the trust ratings of people who trust people who end up being dishonest because you don't know that they were dishonest in their trust of them.

Reputation systems don't work with anonymity. They rarely even work without it.