Free

There are other aspects from Sandel's book that keep flashing through my mind.

For example, if you hold a similar opinion with me and agree money could buy medical service, how about body parts?

No, it goes beyond organ transplant, or even blood donation. Say, you can consider the scenario of using one's body for advertisement. (Michael Sandel does give a vivid case of such in his book.) When we extrapolate the definition of body part, we can also consider the scenarios of trading sex service (that is, prostitute) and privacy (for example, joining a reality game show).

As Sandel points out elegantly, in addition to crowding out the higher non-monetary value of our body and dignity, another major reason against all these is, under most circumstances, the two sides of buy-and-sale are not equal at the bargaining table; the consent of trading could hardly ever be considered voluntary; the choice of selling is not free.

But, as we discussed some weeks ago here, freedom is an elusive concept. After all, does any apple ever fall to the ground freely?