The very fact of a system of exchange system privileges whomever is most able to say no. Max Weber and others have pointed out that this inherently exacerbates economic inequality, ultimately leaving workers destitute while a few get rich.
Admittedly, Weber attributed this to capitalism, but the logic of his argument applies to *any* market system.
The only way to avoid it is to start with a perfectly level playing field and somehow--impossibly--to keep that field level.
Economics that works, then, applies the maxim from the Communist Manifesto: To each according to their need, from each according to their ability.