I'm thinking of a variant of Parfit's Hitchhiker. Suppose the driver lets you in the car. When you get to the city, decision theory says not to pay.
To avoid that result, you can posit reputation-based justifications (protecting your own reputation, creating an incentive to rescue, etc). Or you can invoke third-party coercion (i.e. lawsuit for breach of contract). But I think it's very plausible to assert that these mechanisms wouldn't be relevant (it's a big, anonymous city, rescuing hitchhikers from peril is sufficiently uncommon, how do you start a lawsuit against someone who just walks away and disappears from your life).
Yet I think most moral theories currently in practice say to pay despite being able to get away with not paying.
OK, I think I understand what you're saying a little better... thanks for clarifying.
It seems to me that decision theory simply tells me that if I estimate that paying the driver improves the state of the world (including the driver) by some amount that I value more than I value the loss to me, then I should pay the driver, and if not I shouldn't. And in principle it gives me some tools for estimating the effect on the world of paying or not-paying the driver, which in practice often boil down to "answer hazy, try again later".
Whereas most moral...
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Poster's Note: omg, it felt so weird typing "2012" up there.