a. Just in way of emphasis: economists thus predicted that all (100%) non-monetary economies would be barter economies. Empirical observation has revealed that the actual number of observable cases—out of thousands studied—is 0%.
b. Similarly, the number of documented marketplaces where people regularly appear to swap goods directly without any reference to a money of account is also zero. If any sociological prediction has ever been empirically refuted, this is it.
[...] Meanwhile, all textbooks continue to report the same old sequence: first there was barter, then money, then credit—except instead of actually saying that tribal societies regularly practiced barter, they set it up as an imaginative exercise (“imagine what you would have to do if you didn’t have money!”) or vaguely imply that anything actual tribal societies did do must have been barter of some kind.