There has been quite a lot of scholarly research on reputation system in the last 10 or 15 years; see http://scholar.google.com/scholar?q=reputation+system.
This article looks particularly relevant for Bitcoin:
Reputation Systems for Anonymous Networks
Elli Androulaki, Seung Geol Choi, Steven M. Bellovin, and Tal Malkin Department of Computer Science, Columbia University
{elli,sgchoi,smb,tal}@cs.columbia.edu
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