Joe Pinsker, writing for The Atlantic:
There’s no brand that’s as strongly associated with free samples as Costco. People have been known to tour the sample tables at Costco stores for a free lunch, acquired piecemeal. There are even personal-finance and food bloggers who’ve encouraged the practice. Costco knows that sampling, if done right, can convince people that its stores are fun places to be. (Penn Jillette, of the magic act Penn & Teller, has on more than one occasion taken a woman on a date at a Costco warehouse.) [...] It’s true that free samples help consumers learn more about products, and that they make retail environments more appealing. But samples are operating on a more subconscious level as well. “Reciprocity is a very, very strong instinct,” says Dan Ariely, a behavioral economist at Duke University. “If somebody does something for you”—such as giving you a quarter of a ravioli on a piece of wax paper—“you really feel a rather surprisingly strong obligation to do something back for them.” Ariely adds that free samples can make forgotten cravings become more salient. “What samples do is they give you a particular desire for something,” he says. “If I gave you a tiny bit of chocolate, all of a sudden it would remind you about the exact taste of chocolate and would increase your craving.” I often joke that I eat a full meal whenever going to Costco because of the free samples.