Everyday people die in hospitals because there aren't enough organs available for transplant. In most countries of the world - though not all - it is illegal to sell organs. Governments insist that the motive for donating organs has to be altruistic, it can't be financial reward. The idea of being able to sell body parts makes many people uneasy. But is it time for a policy change: should we be permitted to flog one of our kidneys on ebay, say, for $10,000. If not, why not? Tim Lewens is a Cambridge philosopher and a member of the Nuffield Council on Bioethics.