While “green marketing” has emerged as powerful competitive force, many markets lack clear institutional standards or knowledgeable customers to allow firms committed to sustainable practices to differentiate themselves from opportunistic, green-washing competitors. Within these contexts we propose a firm-level lens based on authentic firm reputation as an important, yet poorly understood, competitive force. Drawing on interview data from the architectural design services context we identify the elements that firms use to communicate their own authenticity, as well as discourage green-washing behavior (...) of peers, and present these elements as the “Diamond” model of authentic green marketing, consisting of: The ability to appear above commercial considerations; The ability to frame production methods as craft; The use of corporate visual identity; and An organization's social network of stakeholders. We conclude by discussing the generalizability and implications of our framework for practitioners as well as opportunities for future research. (shrink)