Роберт Чалдини

First, although the familiarity produced by contact usually leads to greater liking, the opposite occurs if the contact carries distasteful experiences with it.

The customers, mostly well-to-do vacationers with little knowledge of turquoise, were using a simplifying principle—a stereotype—to guide their buying: expensive = good.

Perceptual contrast—the tendency to see two things that are different from one another as being more different than they actually are—is a lever of influence used by some compliance practitioners. For example, real-estate agents may show prospective home buyers one or two unattractive options before showing them a more attractive home, which then seems more attractive than it would have if shown first. An advantage of employing this lever of influence is that its tactical use typically goes unrecognized.

Ethologists, researchers who study animal behavior in the natural environment, have noticed that among many animal species, behavior often occurs in rigid and mechanical patterns. Called fixed-action patterns, these mechanical sequences are noteworthy in their similarity to certain automatic (click, run) responses by humans. For both humans and subhumans, the automatic-behavior patterns tend to be triggered by a single feature of the relevant information in the situation. This single feature, or trigger feature, can often prove valuable by allowing an individual to decide on a correct course of action without having to analyze carefully and completely each of the other pieces of information in the situation.
The advantage of such shortcut responding lies in its efficiency and economy; by reacting automatically to a normally informative trigger feature, an individual preserves crucial time, energy, and mental capacity. The disadvantage of such responding lies in its vulnerability to silly and costly mistakes; by reacting to only a piece of the available information (even a usually predictive piece), an individual increases the chances of error, especially when responding in an automatic, mindless fashion. The chances of error increase even further when other individuals seek to profit by arranging (through manipulation of trigger features) to stimulate a desired behavior at inappropriate times.

The rule says that we should try to repay what another person has provided us

The rule of reciprocation was so strong it simply overwhelmed the influence of a factor—liking for the requester—that normally affects the decision to comply.

Similarly, food servers have learned that simply giving customers a candy or mint along with their bill significantly increases tips; and in a restaurant frequented by international tourists, this was the case no matter the nationality of the guests.

In general, business operators have found that after accepting a gift, customers are willing to purchase products and agree to requests they would have otherwise declined.4

A Japanese proverb makes this point eloquently: “There’s nothing more expensive than that which comes for free.”

As we have seen, there was such a concession: I changed from noncompliant to compliant when he moved from a larger to a smaller request, even though I was not really interested in either of the things he offered.