i dont see why even communism would mean there are no free markets:
in the most basic definitiv communism is (economically) a system in which the working people control the means of production.
this could e.g. be achieved if all companies were work coops - thus workers controlled the companies and therefore the means of production
if we dont change anything else there will still be a free market
please explain to me how if every current company was a workercoop free markets were endangered