• Use terminology and measurement devices to categorize multidisciplinary auditors. • Trials occur between claims to relevance of expertise and claims of bias to expertise. • Regulator creates conflicting roles in mediating interprofessional competition. • Differentiate between supervision and oversight role of audit team leaders. • What happens when conflicting claims and criticisms meet in a regulatory regime?. This paper considers the inter-professional rivalries that took place as the Australian federal government attempted to register a pool of greenhouse and energy auditors and establish a multidisciplinary team structure for emissions-related reporting and trading schemes from 2007-2019. Drawing on the notions of trials (Callon, 1986; Latour, 1987) and criticism in trials (Bourguignon & Chiapello, 2005), we show how the government’s attempts in classifying and determining expert roles and responsibilities from engineering, environmental, and financial backgrounds – with a preference for Big 4 accountants in leadership roles – triggered a series of multi-lateral trials of strength and responsibility, and essentially failed to meet its original purpose. By following the regulatory process, we articulate how terminology and measurement devices were mobilised by the regulator to enrol mixed expertise. We also examine how the envisaged identities, roles, and responsibilities were received by lobbyists from the three expert groups, and then how their concern, criticism, and resistance were acted upon and reacted to by the regulator. Our study reveals the dilemma the non-expert government faced in mediating the conflicting interests and goals while fulfilling its regulatory and administrative roles. Our nuanced evidence shows how accounting team leaders role of supervision rather than oversight evoked further controversy. The study contributes to understanding what happens when conflicting knowledge claims and criticisms meet in a multidisciplinary regulatory regime.