From wikipedia:
Contrary to popular conception, there is no evidence that societies relied only on barter before using money for trade.[73] Instead, non-monetary societies operated primarily along the principles of gift economics, and in more complex economies, on debt.[74][75][76] When barter occurred, it was usually between strangers or would-be enemies.[77]
And you forgot: slavery. Sparta basically enslaved surrounding hellenic population ( so called hellots ). Many Athenian politicians were quite disgusted with the harsh conditions Spartans enforced on hellots. Basically they maintained “population control” by slaining hellots en masse when their population grew too much ( Spartans were somewhere around of 10-15% of their dominion )