A system with truly "free markets" in a hypothetical economic system will have perfect competition [1], which includes zero cost to enter and exit markets, large numbers of buyers and sellers, rational buyers, perfect information, and profit maximization of sellers (among other attributes). In this hypothetical model sellers cannot capture excess value because competitors will take that opportunity to capture larger market share.
Excess profit capture represents market failure or disruption.
[1]: https://en.wikipedia.org/wiki/Perfect_competition