Markets in human body parts arise from a contradiction: society forbids treating the body as merchandise, while each person urgently wants to live longer and better. When those two forces collide, the trade doesn't stop; it goes underground.
Bodies are not ordinary goods, because a transfer of flesh carries the value of a life and creates a lasting debt between giver and receiver. A plain free market in body parts hides where the parts came from and prices a person at their raw material value, so legalizing sales is no simple fix.
Police and international law can shut down particular body-part rings, but medical advances keep expanding what human tissue is useful for, from ligaments to kidneys to rented wombs. Growing demand outpaces enforcement, so the trade falls, then returns, and the ethical questions get skipped.
Once body parts move through a paid supply chain, 'donor' is a misleading word: the people giving them up are usually poor and are paid or pressured. Talk of generosity covers the money and the people who need it.
The proposed safeguard is radical transparency: every human part in the supply chain should be traceable to the person it came from. Making the source visible keeps the human being from disappearing behind the transaction, though it will not solve every problem.