Citizen science is currently at the forefront of environmental scientific research and public policy for its potential to improve environmental governance, restore epistemic trust and help address some of the most stressing environmental challenges. Although citizen science is gaining increasing popularity, there is little empirical evidence to support these claims and demonstrate how bottom-up citizen science shapes public trust in environmental governance and science. In this paper we reflect on three grassroot environmental citizen science initiatives in Cameroon, Japan, and the UK to identify and present an instrumental framework which includes trustee attributes and conditions that influence how epistemic trust is shaped, and which should inform citizen science and other participatory practices. We explain that citizen science is an approach which enables political processes through the construction of well-informed techno-scientific arguments, which expose deficit assumptions about the public’s ability to participate in knowledge co-production process. To avoid repeating the failures of the past and risk amplifying issues of public distrust further, we provide suggestions built around key trustee attributes which can be incorporated in citizen science practices and we urge that environmental policy needs to create clear policy frameworks to enable the generation of actionable data, especially when such approaches are initiated and implemented as instrumental public participation methods.