Ashraf, Gine, and Karlan, "Finding Missing Markets (and a Disturbing Epilogue): Evidence from an Export Crop Adoption and Marketing Intervention in Kenya," Amer. J. Agr. Econ, Vol. 91, (4), 973-990, ungated.
A Kenyan NGO helped farmers move into export crops [French beans, baby corn, or passion fruit] and lowered their marketing costs. This increased adopter income by 32% ... until EU production requirements changed a year later adding $581 costs per farmer and shut them out of the market. Ouch. Methods: clustered randomized control trial to determine the difference adding agricultural credit to their package of extension and marketing services.
"Other similar interventions include the use of mobile phones to obtain real-time prices for fish in markets along the shore by boat owners returning with their catches (Jensen 2007) and an intervention in India to provide internet kiosks in small villages in order to better inform villagers of market opportunities (Upton and Fuller, 2005; Goyal, 2008)."
Adding agricultural credit makes a farmer 19% more likely to grow an export crop and more of their land is used for export crops; and increases production (kg) for baby corn, but not for French beans (all extra-marginal).