The purpose of the book is to make the general-audience reader realize the problems with the conceptual-historical framework of neoliberal economics and politics. David Graeber rightfully argues that Neoliberalism sells itself to the masses by constructing this "quaint" tale of uncivilized barter-practicing foraging tribes turning into coin/money using farmers into debt based industrial-financial empires.

I am sure there are many factual inaccuracies in the book (I am not an expert so I wouldn't know either way). But what he successfully manages to do is show the reader that there are many many different economic systems practiced throughout history, and many of them very highly sophisticated (and not quaint as you suggest). And once the reader realizes this, there is only a short step to the question, "is neoliberalism really the best we can do or one of the other systems better for us?"