This blog post has been updated and moved to https://www.justinkhughes.com/jog.
References (the first two describe reciprocity):
Influence by Robert Cialdini
Business Networking that Works: It’s Called Quid Pro Quo by Forbes
Love and Respect by Emerson Eggerichs
Getting the Love You Want by Harville Hendrix
The Seven Principles for Making Marriage Work by John Gottman