Their reference to hotel room cleaners who leave their names in the room is an example of an attempt to change the guests's preferences as applied to a specific individual. Social capital is a coefficient on own and other's welfare in one's utility function which is an evolving function of the relationship and affinity between the parties. The authors illustrate it when they observe that allocators in dictatorship games offer more of the pot to friends than strangers. The value of other's income in the allocator's utility is a function of affinity. And, if the other person signals their lack of affinity for the allocator or the responder, the behavior is different.
People learn and are reinforced within the transaction as well as outside.
Handbook of Behavioral Economics, Vol. JAI Press, 1991. Staff Paper No.