人情 Human feeling. Also a favor, or a gift. 做个人情, to do someone a favor.
卖人情 To sell a favor. To do someone a good turn on purpose, so that they feel grateful. A dictionary gives the example: “If you sell him a favor today, he will surely repay you in the future.”
人情世故 Human feeling and the ways of the world. The knowledge of how to deal with people.