We report the importance of informal training in introducing new post-harvest technologies in rice farming through informal contacts by exploring answers from both in-residence extension workers ('key farmers') and ordinary farmers in rural Cambodia. We use survey data collected in Cambodian villages between December 2012 and January 2013. While in-residence extension workers are well motivated and informal training plays a crucial role, lack of an appropriate financial incentive for the key farmers might hamper the sustainability of the project. We also emphasize that any intervention for rural development must avoid social exclusion and nepotism.