Many companies (Bubble Island, 7/11, Starbucks, Espresso Royale) have loyalty programs. They have promotions saying things like "Buy 7 drinks, get the 8th free" or "Earn reward points by shopping online". In this way, they acknowledge your purchases and show tangible gratitude. In turn, you want to buy more products, to receive more rewards. This appreciation in turn the boosts sales of the company. Although the core of the marketing tactic was rooted in increasing profits of the company, maybe the reason it works so well is because people like to feel appreciated and a rewards program is the perfect way to do so.