The definition of capitalism seems to be the biggest problem when anarchists and 'anarcho-capitalists' debate. People exchanging mushrooms for berries isn't capitalism, it's just trade. Capitalism arose out of the process of primitive accumulation, wherein people were dispossessed of their land and means of production, with nothing left to do but sell their labor. Capitalism doesn't exist without an accumulation of capital, a bunch of dispossessed people, and a bunch of guns and steel cages (and cultural programming).
Now I suspect when you scale this idea into 'individuals attempting to maximize their well-being by exchanging value for value to meet human needs', you are talking about something very different (assuming you are an 'ancap'). Wage labor? Private property? Interest, rent, profit.......
Check these out:
http://anarchism.pageabode.com/afaq/secF8.html
http://anarchy101.org/25/why-does-capitalism-rely-on-the-state
http://anarchy101.org/6/how-can-there-be-anarchocapitalists-and-anarchocapitalism
(edited to remove faulty definition of market. see funkyanarchy's comment. thanks!)