Gift Giving and the Mandate of Reciprocity: Abraham and Marcel Mauss

(Something to think about before Hanukkah's gift exchange...]  I read Abraham's penchant for gift giving and hospitality --and his contrasting refusal to accept a discount from the Hebron locals for the prime burial cave-- through the lens of French-Jewish sociologist Marcel Mauss's book The Gift: The Form and Reason for Exchange in Archaic Societies, his landmark study of the centrality of gift giving in tribal societies. (The book became highly influential on French literary theory, and Mauss himself was the founder of the French Academy for Sociology, along with his famous uncle and mentor, Emil Durkheim, also Jewish, whose Elementary Forms of the Religious Life --which focuses on religion as a community, not a faith, phenomenon-- is still a required classic in the field of religion today.)  What's the difference between systems of gift exchange and of money/barter exchange?  What different obligations are involved?  What does it mean to accept a gift, even today?  What cost is there to chasing sales and Black Friday discounts?  And how does this relate to the Lubavitcher Rebbe's comment that "Abraham knew that nothing comes for free?" (Comments from participants have been edited out as they were not picked up by the microphone.)