The answer beginning, "Suppose that A and B exchange with each other" is unreferenced and factually inaccurate. The story being told in that answer has been known to be false for 100 years.
Here is a constructive critic of Graeber affirming this:
As Graeber explains, however, pure barter as such never existed. The myth of barter is a
handy story for explaining the origins of money in terms that warrant market theories
of price and commodity exchange. But, historically and ethnographically, it does not hold water. None of this is news to anthropologists. It is, after all, the basis of Mauss’s analysis of The Gift.
Bill Maurer, “Debating Anthropology's Assumptions, Relevance and Future: David Graeber's Wunderkammer, Debt: The First 5,000 Years,” Anthropological Forum 23(1)
The book cited is The Gift by Marcel Mauss, a classic of anthropology published in 1925. Mauss' analysis of pre-monetary gifting is now widely used by historians in order to prevent the simplifications that the modern concepts of barter and currency can create. For example, I just read an excellent book, The City-State of Boston 1, which discusses to great effect how the early American gift material called wampum was neither money nor barter, and how its uses changed with the arrival of economically interested European settlers.
The critique of Graeber made in the article being quoted does not come from debunking the myth of barter, which is unquestioned among social scientists, but from the question of how the myth of barter arose.
and barter-commodity theories did, alternately and often cyclically, as Graeber
demonstrates in the second half of the book, rise to prominence, capturing the imagination of noble and patriarch, king and parliament, authors and activists alike. In so
doing, they conjured a world after their own image. The theories properly speaking
do not describe, they perform. But that performing
makes difficult the quest for origins with which Graeber begins his analysis: the
origins of the ethical imperative to repay a debt.
ibid., emphasis added
This goes beyond the scope of this question, but basically, Graeber is correct to reject the myth of barter which appears on the "Library of Economics and Liberty" and other such untrustworthy websites. The major concern with his book is his account in how the concept of personal debt and the myths of barter and state credit arose, which complicate the issue.
- The City-State of Boston: The Rise and Fall of an Atlantic Power, 1630–1865 by Mark Peterson – April 23, 2019 - Amazon Link