Since pervasive computing applications are mostly designed to enhance existing social situations, such applications should take ac- count of the trust relationships within the situation in their design. In this paper we describe the ethnographic approach we used to explore how trust is formed and maintained within a farmers market, and how this understanding can be applied in the design of supporting applica- tions. We then evaluate the applications using the same ethnographic approach, uncovering problems which would not have been visible with other evaluation techniques.