
People are more likely to give change for a parking meter to a complete stranger if that requester wears a uniform rather than casual clothes. Physiotherapists, for example, are able to persuade more of their patients to comply with recommended exercise programs if they display their medical diplomas on the walls of their consulting rooms.

This is the idea that people follow the lead of credible, knowledgeable experts. Our Third Principle of Influence is the Principle of Authority So the key to using the Principle of Reciprocity is to be the first to give and to ensure that what you give is personalized and unexpected. A 23% increase, influenced not by what was given, but how it was given. But perhaps most interesting of all is the fact that if the waiter provides one mint, starts to walk away from the table, but pauses, turns back and says, “For you nice people, here’s an extra mint,” tips go through the roof. Interestingly, if the gift is doubled and two mints are provided, tips don’t double. In the study, giving diners a single mint at the end of their meal typically increased tips by around 3%.

But that mint can make a surprising difference. Does the giving of a mint have any influence over how much tip you’re going to leave them? Most people will say no. A liqueur, perhaps, or a fortune cookie, or perhaps a simple mint. Probably about the same time that they bring your bill. So the last time you visited a restaurant, there’s a good chance that the waiter or waitress will have given you a gift.

One of the best demonstrations of the Principle of Reciprocity comes from a series of studies conducted in restaurants.

And in the context of a social obligation people are more likely to say yes to those who they owe. If a colleague does you a favor, then you owe that colleague a favor. If a friend invites you to their party, there’s an obligation for you to invite them to a future party you are hosting. Simply put, people are obliged to give back to others the form of a behavior, gift, or service that they have received first. The First Universal Principle of Influence is Reciprocity
