Here is how the norm of reciprocity works: If you are kind to me, I will be kind to you in return—and vice versa. According to this norm, people have a fundamental need to reward kindness and punish unkindness. Negotiators benefit from including this behavioural regularity into their toolbox. In many situations, we can trust each other because we know that the norm of reciprocity obligates trustworthiness in return.

Reciprocity does not come cheap. Invitations to reciprocate work best if they are based on an intentional act of true generosity. What is considered to be kind or fair and thus worthy of reciprocation depends on the specific context in which a negotiation takes place. One of the most important features of the context determining fairness reference points is whether or not social comparisons are possible. What may seem to be a stingy offer in isolation, can be perceived as fair when compared to comparable offers.

Experienced negotiations know this well. Retailers lure buyers by offering a discount off what they hope to establish as the norm, the manufacturer’s list price; salespeople seek to convey the impression that their buyer of the moment is getting a special low price; and proposers of marriage try to convey the impression that the responder is regarded more highly and loved more dearly than anyone the proposer has ever met. Both parties know that if the proposal is viewed as being favourable relative to the norm, the prospects for acceptance are considerably enhanced.

Here are some strategies that help you employ the norm of reciprocity effectively:

1. Clearly establish who the parties to the reciprocal exchange are. If the parties at the table are negotiating on behalf of someone else, you need to know whether or not they are empowered to engage in the game of reciprocity.

2. Make sure your behaviour cannot be attributed to ignorance or chance. Study comparable offers (demands) before you meet at the negotiating table and let your counterpart know that you are informed and intentionally make the offer (demand) you put on the table.

3. Make your counterpart feel indebted. Only a meaningful favour induces kindness in return. For example, patterns of concessions may signal your expectations of reciprocity. To signal your willingness to cooperate, make a relatively large concession initially but do not move if your counterpart does return the concession.

4. Send a credible signal. Credible signals cannot easily be faked. For example, blushing is a credible signal of embarrassment. If it is known that someone tends to blush when lying, it becomes a credible signal of truth-telling.

5. Find out how your counterpart feels about reciprocity. Will she turn down a favour because she does not want to be obliged to return it? Will he be upset when invited to reciprocate or will he be distressed if prevented from returning a favour? What cultural or context-specific norms of reciprocity apply?

6. And finally, and probably most importantly, make it attractive for your counterpart to reciprocate. Increase the benefits—material, psychological, social—of norm compliance. Build a relationship, make the kindness of your offer (demand) publicly known and engage in repeated interactions where reciprocating your kindness is also in your counterpart’s long-term interest.