When addressing socio-scientific wicked problems, there is a need to negotiate across and through multiple modes of evidence, particularly technical expertise and local knowledge. Democratic innovations, such as deliberative citizens’ juries, have been proposed as a means of managing these tensions and as a way of creating representative, fairer decision making. But there are questions around participatory processes, the utilization of expertise, and deliberative quality. This paper considers forms of argumentation in the 2013-2014 “Citizens’ juries on wind farm development in Scotland.” Through a critical-interpretative research methodology drawing on rhetoric and argumentation, we demonstrate that arguments relating to the topoi of the environment and health functioned as de facto reasoning, whereas arguments using social scientific evidence around economics more prominently interacted with local knowledge. The findings offer implications for process design to improve and promote deliberative quality in mini-publics and other forms of participatory engagement on socio-scientific issues.