Hal writes:
Changing the market conventions (say, by introducing escrow agencies) will change the weightings of the various factors that make up utility. If I no longer have to trust the honesty of the person I am trading with (because we have an escrow agency to help us make the exchange) then the importance of his reputation for honesty goes down. The result is that the "reputation" curves will change rather dynamically and unpredictably as we consider different possible structures in the market. This will make the analysis of them intractable, I would think.
Analytically, using an escrow agent doesn't change the utility function. It replaces the trading partner's honesty reputation estimate with the escrow agent's (which is presumably higher, or why use them?). This is just a parameter substitution. Whence comes the intractability?