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An interesting question. Methinks this whole "trust"business is an attempt of the "embourgeoisment" of a debate on the role of social institutions in economic transactions. Some time ago Oliver Williamson argued that high transaction costs of market exachanges make "hierarchies" (i.e. complex organizations) more efficient in a comparison. His criticics argued that it is not "hierarchies" (i.e. formal supervision) per se, but social relations, networks, expectations etc. they entail that save transaction costs.
Of course the neo-classically processed crowd cannot swallow anything that even remotely smacks of social institutions, so they had to steer the debate back to the individuals and their "human nature." Consequently, they came up with this bullshit concept of trust - a cognitive/attitudinal disposition that prevents economic actors from engaging in opportunistic behaviour in high-information-asymmtery situations.
Although there have been some hints that trust might be socially constructed (cf. Putnam or Fukuyama) - social constructivism is the most outrageous blasphemy to the neoclassically processed crowd, because it implies that economic institutions, especially the Holy Market, are socially constructed rather than 'natural.' As Marx somewhere noted, bourgeois political economy is like religion, everyone else's is man-made, only ours is god-given. Any hint of social constructivism undermines the capacity of the neoclassical theory to serve as civil religion of the capitalist state, a legitimating ideology for the status quo.
In other words, the concept of trust is a nod that other than purpose-rationality factors may be a factor in economic decision making - but it is a concept that stays well within the cognitive/attitudinal realm of the individual and thus hedges against bringing social institutions into economic discourse.
regards,
Wojtek