Reciprocity

What it is

Feeling obliged to return favours, gifts and concessions, even small or unrequested ones.

Example A free sample makes you feel you should buy.

Commitment and consistency bias
Accepting a favour is a commitment that we then feel bound to match.
Liking bias bias
Doing favours increases liking, and liking increases our willingness to return favours.
Lollapalooza effect bias
Reciprocity is one of the tendencies that can stack with others for extreme effect.
Kantian fairness tendency bias
Fairness norms and reciprocity norms make people give as well as receive.
Motivation crowding bias
Reciprocity relies on a norm of gifts and favours that payment can replace with a market norm.