I'm not sure what you're trying to say. Are you saying an unencumbered free market system is impossible, or just that it's not what our current system is right now?

If the latter, I agree; that was sort of the whole point of my comment. Amazon controls a large portion of the shipping market, therefore what we have here is closer to a monopsony than an unencumbered free market.

If the former, I mostly disagree. Obviously a perfectly idealized free market system is impossible in the real world: all idealized systems are. There's no such thing as a frictionless surface or a perfect sphere either. That doesn't mean however that we couldn't be a lot closer to that ideal than where we are now, or that idealized systems aren't useful tools for modeling the behavior of similar, non-idealized systems in the real world.