There is no human society that does not subscribe to the rule, the author writes. In fact, it is only because our ancestors learned to share food and skills in an honored network of obligation that we are human, says anthropologist Richard Leakey. Studies show that reciprocity overpowers dislike. A business example of reciprocity is free samples. There's a reason you can eat a small meal while walking the aisles of Sam's Warehouse Club.
Free samples sell product.
Another way to employ reciprocity is somewhat more indirect. You can make a concession. For instance, if you start a negotiation with a high asking price, then reduce that price, you have made a concession. The party with whom you are negotiating will likely respond with a concession. The author tells a marvelous story about reciprocal concessions at work.