"because they are attached to an individual and form the basis for whether they can be trusted and accepted. A reputation is really the collection of tags that are assigned to an individual or entity to reflect assessments of their competence or status within a specific social network. Given that individuals play different roles in social networks - they can serve variously as connectors, gatekeepers, truth-tellers and enforcers - reputations are tied to roles within social networks.
It is not difficult to see how important reputation tags are in small traditional societies where once a reputation is acquired, it may be very difficult to change. Honor-based societies depend upon reputation tags as the principal governance mechanism for defining and enforcing a social order. "Honor killings" of a daughter or sister in order to preserve a familiar reputation suggest the power of reputation in Human Nature. Even in online communities, reputation tags are the motivator and governor of behaviors. People take seriously the reputation scores of an eBay seller/buyer, the accumulated scores of a player of online games, or the number of friends and ratings one has in the online social networks of Linkedin, Orkut, Friendster, Facebook, or My Space.
Reputation tags affect an individual or group's ability to participate within and across different networks, thereby becoming the basis for granting/revoking certain privilege and decision rights. Since reputation tags can be measures of competence by a socially credible third party - e.g., religious, educational, financial, political, trade or professional institutions - they play a very powerful role in governing social mobility and enabling/thwarting interactions between different social networks. By providing information about information - who or what it is, where it came from, as well as marking the rights and privileges for accessing, exchanging, altering, or forwarding goods, services and information, tags are the true control points in self-organizing networks." (http://onthecommons.org/node/723?PHPSESSID=97029cd7f7a249340f4973b4dceaee3a)