Some of these books are:
Go-givers sell more by 
The go-giver : a little story about a powerful business idea by 
Free by 
Give and take : a revolutionary approach to success by 
The Generosity Factor by 
Influence : the psychology of persuasion by 
Wired to care : how companies prosper when they create widespread empathy by 
Reciprocity : an economics of social relations by 
Handbook of the economics of giving, altruism and reciprocity by 
The helping relationship : process and skills by Click to see over 14 magazine articles on reciprocity or generosity in interpersonal relations.
Click to see over 100 academic journal articles on reciprocity or generosity in interpersonal relations.
Some journal articles are: