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JStewart comments on Circular Preferences Don't Lead To Getting Money Pumped - Less Wrong
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Comments (19)
Having circular preferences is incoherent, and being vulnerable to a money pump is a consequence of that.
This means that you won't, in fact, trade your X for .95Y. That in turn means that you do not actually value X at .9Y, and so the initially stated exchange rates are meaningless (or rather, they don't reflect your true preferences).
Your strategy requires you to refuse all trades at exchange rates below the money-pumpable threshold, and you'll end up only making trades at exchange rates that are non-circular.
This is only true if your definition of value compels you to trade X for Y if you value Y more than X in the absence of external transaction costs. A simpler and more clearly symmetric definition would be, if given a choice between X and Y, you value Y more than X if you choose Y and vice versa.
An otherwise rational agent with hard-coded pairwise preferences as in the OP would detect the cycle and adjust their willingness to trade between X, Y, and Z on an ad hoc basis, perhaps as an implicit transaction cost calculated to match expected apples to apples losses from future trades.