That isn't the alternative. The alternative is people get in debt with each other, which is what happened historically. People simply didn't spot trade with their neighbors. The spot trade is a property of state created markets.
Trading in debt isn't an alternative to markets, it's a market with debt as the currency. Regardless, the "spot trade" as you put it is also older than nation-states, not something they created.
I've seen it, and didn't find it very convincing. Graeber presents some interesting anecdotes regarding selected ancient social conventions, which may or may not be accurate[1], but—in my opinion—even taken at face value they don't really support his conclusions regarding the nature of debt. Perhaps the book would seem more compelling to someone who already shares the author's worldview.
