In payment for ecosystem services (PES) models, participants receive payments for conditionally securing the provision of ecosystem services. Nevertheless, various constraints and complex local contexts, common in realworld PES schemes, impede a perfect implementation of the model. I examine how fieldworkers implement PES given financial and monitoring constraints, using the case of the Bolsa Floresta program in the Brazilian Amazon, a policy instrument that pays 50 Brazilian Reais to participating families if they do not deforest primary forests. Building on in-depth interviews and participant observation, I argue that fieldworkers’ actions reveal deviations between PES theory and practice. They use their discretion at the local level to (1) adopt discursive practices that underemphasize the economic component of Bolsa Floresta and complement it with a pedagogical element, and (2) adopt trust-building practices based on organizational routines and boundary-making vis-`a-vis commandand- control authorities. This deviation from PES theory implies that different policy instruments require different levels of trust depending on their coerciveness. My fieldworker-oriented approach complements PES scholarship by tying environmental fieldworkers’ routines and practices at the implementation level to strategies to address some common limitations of PES schemes.