I am 2 chapters into "Influence: The Psychology of Persuasion", 1984, Robert B. Cialdini, Ph.D. It is often referred to in the literature on sales and maketing so could be considered a classic in these areas. It is a well crafted book with lots of research reported and cases analyzed with respect to what pursuasion principle is being invoked to cause people to buy a product or service (or otherwise act in a compliant manner).

Chapter 2 of the book deals with the principle of reciprocity and the many ways in which it can be used as a sales tool. The best illustration of reciprocity in action is a social psychology experiment Cialdini reports in which subjects were asked to rate paintings. During a 2 minute break period, one of the "subjects", who was really a part of the experiment, comes back into the lab area with two Cokes and offers one of the Cokes to a fellow subject saying "I asked him [the experimenter] if I could get myself a Coke, and he said it was okay, so I bought one for you, too". In half of the cases, he did not offer a favor to fellow subjects. In all other respects, the planted subject was scripted to act the same.

What they were investigating was how many raffle tickets the planted subject would be able to sell to the person s/he offered the favor to as compared to the person s/he did not offer a favor to. The planted subject sold twice as many raffle tickets to the people she offered the favor to.

The reciprocity technique is on display when free food samples are offered in grocery stores. If we take the sample, we feel more obligated to consider buying the full product. You may avoid taking the "free" sample because you don't want to feel any obligation to, or feel compelled to, buy the full product. The impulse to reciprocate is what may be driving these feelings of obligation or compulsion.

It is worth reflecting on whether you can use the reciprocity impulse to enhance your sales effort.