Suppose you want to find out the answer to a binary question, such as ‘would open borders destroy America?’, or ‘should I follow this plan?’. You know someone who has access to a lot of evidence on the question. However you don’t trust them, and in particular, you don’t trust them to show you all of the relevant evidence. Let’s suppose that if they purport to show you a piece of evidence, you can verify that it is real. However since they can tell you about any subset of the evidence they know, they can probably make a case for either conclusion.  So without looking into the evidence yourself, it appears you can’t really employ them to inform you, because you can’t pay them more when they tell the truth. It seems to be a case of ‘he who pays the piper must know the tune’.

But here is a way to hire them: pay them for every time you change your mind on the question, within a given period. Their optimal strategy for revealing evidence to make money must leave you with the correct conclusion (though maybe not all of the evidence), because otherwise they would be able to get in one more mind-change by giving you the remaining evidence. (And their optimal strategy overall can be much like their optimal strategy for making money, if enough money is on the table).

This may appear to rely on you changing your mind according to evidence. However I think it only really requires that you have some probability of changing your mind when given all of the evidence.

Still, you might just hear their evidence, and refuse to officially change your mind, ever. This way you keep your money, and privately know the truth. How can they trust you to change your mind? If the question is related to a course of action, your current belief (a change of which would reward them) can be tied to a commitment to a certain action, were the period to end without further evidence provided. And if the belief is not related to a course of action, you could often make it related, via a commitment to bet.

This strategy seems to work even for ‘ought questions’, without the employee needing to understand or share your values.