Ah, yes. Thanks for clearing that up.

In this particular case, then, I don't see what lies they could have profitably told. The situation was very symmetric, and falsifications of the utility function would kind of stand out.

In other cases, yes, that's a problem. In the case where everyone can verify what everyone really needs or normatively should need*, then this works a lot better.

*I mean the case where, say, a company would benefit from more secrecy, but only at the cost of keeping effective medicines off the market. If they object on the ground of profit, the rest of the community can rightly give them the finger. And any alternative justifications for secrecy they offer will be subjected to additional scrutiny because everyone can see how it'd benefit them specially.