See, not as simple as it sounds.
If there are no boundaries or rule structures, then the incentives often (always?) bleed into some involved party not having a choice, or a Hobson's choice.
Someone having to choose between selling a kidney or starving is terrible. But the solution shouldn't be to deny the first option - that just leaves starving. It should be to give them a third option.
That said, obviously "no rules" would still be dangerous, but no legal sale is done without any rules.
There's little reason for anyone to submit to organ harvesting to eat. The idea that our society is just enough for individuals to face that choice is kind of laughable.
Of course the best thing is to make artificial organs work, but that's not something most potential organ donors have much influence over.
If in the XXI century we have not eliminated those dilemmas is that we are doing something wrong.
Also, it seems that you would be creating an incentive to make people hungry.