"Free market" doesn't mean the parties have equal bargaining power (no two parties in the world do). It means that the parties are free to bargain directly with one another, without a third party (i.e. government) injecting the interests of those not party to the bargain.

A free market allows a farmer to trade barley with a buyer from another nation - an unfree market sees the government(s) disallow this due to protectionist policies lobbied for by unrelated farmers who benefit from decreased competition.