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
The Jog 