We will first present what the reviewed literature says on the impact of supermarket development on farmers in terms of the different requirements involved, especially in terms of quantity and quality, then we will investigate the impact on traders, and finally some recommendations for public intervention. In Costa Rica, modern retailers are said to prefer local small-scale retailers rather than large farmers who may more easily shift from one customer to the other, especially to sell to exporters. Hortifruti is committed to buy beans locally, although import prices are lower: 70% of beans sold are bought from local small farmers (Balsevitch et al, 2004 and Rondot et al, 2005).