The power of positive feedback
As my students inevitably discover each semester, I'm a huge fan of research in primate psychology. Arguably my favorite experiment is this inquiry into proto-human concepts of justice. In a nutshell, monkeys were taught to exchange tokens for food, but when a monkey thought the exchange was unfair--say, a monkey getting a cucumber in exchange saw another getting a grape--the monkeys getting the comparative raw deal would indicate their dissatisfaction by essentially going on strike.
A savvy do-gooder can do a lot with the basic insight of such research: namely, that primates tend to shy away from transactions lacking in sufficient value-added. Consider a promotion that recently showed up on JustMeans: Campbell's student "Can Hunger" Challenge. The contest--a competition that rewards students for gathering food for charity--is just the latest variant on a decades-old marketing strategy through which Campbell's has enmeshed itself in the U.S. educational system.
Campbell's has trained parents across the country to see budget soup in terms of a fairness-laden choice: buying Campbell's provides soup & some form of benefit for the school; buying a competitor's product just leaves you with soup. The result: a systemic aversion from competitors' products that has made Campbell's a market standard at its price point--in comparisons between soups of similar cost & quality the competitor becomes the cucumber while Campbell's is the grape.