Purchasing food at farmers markets (FMs) has seen increasing popularity over the last decades due to assumed locality, short supply chains and seasonality of food products that together may reduce the ecological footprint of private consumers. But the empirical evidence about the motivations for and barriers to purchasing food products at FMs is often based on data from small samples with regional focus assessed at one point in time and therefore depict only an incomplete picture of the true nature of the underlying preferences. This study uses two mixed-mode surveys to overcome these disadvantages and puts special emphasis on the analysis of the behavioral mechanism that influences the decisions to reveal individual preferences food purchases at FMs. In particular, our main analysis uses four waves of the GESIS panel, a probability-based access panel representative of the population of Germany. We are able to use repeated measures of purchasing decisions and model the impact of situational opportunity structure, internal constraints as well as social expectations while controlling for seasonal variation in consumer behavior. We find that behavioral costs are of utmost importance when preferences for local and sustainable food products are to be revealed at FMs, while social expectations appear to be more important drivers for purchasing decisions at FMs than internal constraints such as environmental attitudes or health concerns.