Earlier quoted context omitted.
Nobody has ever found a better way. What you're willing to pay for something determines its value to you.
The assumption that price paid == utility is only valid in the economic equivalent of "assume no friction" from intro-level physics. The equivalence isn't guaranteed to hold once you bring individuals' budget sets and various market distortions into play (information problems, sticky prices, et alia). You see the same thing on the supply side, with the assumption that price sold == marginal cost breaking down in gene…
Supply + Demand determine the value.