Do people feel indebted when they receive a free sample and are therefore more likely to buy?

Question

Robert Cialdini claim in his book Influence that one of his six principles is the principle of reciprocity. It means that if you do a small favor to someone they will feel indebted to give you something back.

In the book he gives the example:

Of course, the power of reciprocity can be found in the merchandising field as well. Although the number of examples is large, let’s examine a pair of familiar ones. As a marketing technique, the free sample has a long and effective history. In most instances, a small amount of the relevant product is given to potential customers to see if they like it. Certainly this is a legitimate desire of the manufacturer—to expose the public to the qualities of the product. The beauty of the free sample, however, is that it is also a gift and, as such, can engage the reciprocity rule. In true jujitsu fashion, a promoter who provides free samples can release the natural indebting force inherent in a gift, while innocently appearing to have only the intention to inform.

Is there academic research that this effect replicates? That giving a free sample does more than just exposing the customer to the virtue of the product? That the customer is more likely to buy the product because they feel like the have a debt to repay?

Answer 1

Yes, this is a part of reciprocity theory:

Over the past forty years, numerous studies in social psychology offered empirical support to reciprocity theory. Major findings can be summarized as follows: Receiving even a small favor leads to further compliance with requests of the person who provided the favor (Howard, 1995), even when the favor is unsolicited and unexpected (Regan, 1971), and even when a favor-giver is not perceived as likable (Goei, Massi Lindsey, Boster, Skalski, and Bowman, 2003). Receiving a favor in public conditions creates greater compliance than receiving a favor in private conditions (Whatley, Webster, Smith, and Rhodes, 1999). As the amount of time lengthens between the initial favor and the opportunity to reciprocate, the perceived need to reciprocate diminishes (Burger, Horita, Kinoshita, Roberts, and Vera, 1997).
_{Gender as a Moderator of Reciprocal Consumer Behavior}

Additionally, DavePHD's comment is also supported by research. Several studies have been done on wine tasting, one of which says:

The results of the current study empirically supported previous experimental evidence that people feel appreciation and a need to reciprocate for what they have received. Therefore, if winery visitors find their experiences at wineries enjoyable, they are likely to develop a sense of gratitude and possibly a sense of obligation to return hospitality provided by the winery personnel. These feelings, in turn, may lead to a perceived need to buy wine or wine souvenirs at the end of their visits.

Additionally, the study aimed to investigate whether visitors of smaller and larger groups differ in terms of the amount of money they spend at wineries and with respect to feelings of gratitude and obligation. The results indicated that visitors who travel to wineries in smaller groups feel more grateful to winery personnel and more obliged to buy wine than those visitors who traveled in larger groups. Accordingly, visitors who travel in smaller groups tend to spend more money on wine than larger groups.
_{IMPORTANCE OF WINERY VISITOR GROUP SIZE ON FEELINGS OF GRATITUDE AND OBLIGATION}

And a similar thing happens with pharmacists who receive free samples and other gifts:

A research published in the American Journal of Bioethics in 2003 [18] points out to the fact that physicians prescribe more medication to which they have access to free samples donated by representatives. Massud [15] confirms this finding by affirming that physicians who receive samples prescribe less and less generic medications and consequently contribute to the increase of expenses with medication.
_{Physicians and Conflicts of Interest}