"In the absence of a third party with a gun I can't see how or why two people would choose to enter into a trade that don't benefit at least one of them, and probably both."
Well, at least that they don't both believe will benefit them.
Well, at least that they don't both believe will benefit them.
It really depends on who you are. There's no way to have an objective arbiter who determines what is actually beneficial and what merely seems to be beneficial. At least that I know of. The problem seems intractable to me.