Costco is probably one of the most well known retailers employing free sample marketing strategies. It is a well known practice, even encouraged on blogs, to cruise the sample stations for a "free lunch". There is evidence that free sampling opportunities not only help consumers learn more about products, it also make the retail environment more appealing. Costco itself does not manage the sample stations. A product demonstration company is responsible for staffing the sample tables.
Behavioral economists state that getting something for free creates a strong feeling of obligation to do something back. (ie. buy the product you just sampled). Free samples can also make forgotten cravings become more evident to the consumer, causing the consumer to feel compelled to act on the craving. One interesting fact from sampling research showed that it is important for the demo table to be staffed (vs. self serve). A heightened awareness of the presence of others increases the "social pressure" to make a post-sample purchase.
In addition, the prepared food departments in stores for eat in and carry out, including the "cafe" at Costco, are designed to make the store a destination for eating a meal. Once in the store, there is a greater likelihood of the consumer buying additional products while at the store. At the very least, eating a meal at the store increases the positive experience of the customer, making it more likely that they will return to the establishment at a later date.
You can read more details about free sample marketing strategy by visiting the links below.
http://www.theatlantic.com/business/archive/2014/10/the-psychology-behind-costcos-free-samples/380969/
http://www.marketingweek.co.uk/trends/offering-a-bit-more-than-a-free-sample/4001841.article
http://business.time.com/2011/02/17/the-power-of-freebies-why-companies-pay-to-give-free-samples-to-supermarket-customers/