The choice of incumbent financial auditors to provide sustainability assurance and audit services from a legitimacy perspective
Authors: Ruiz-Barbadillo Emiliano , Martínez-Ferrero Jennifer 
Published: October 2021

Purpose
Sustainability assurance services are carried out in a competitive market where a wide range of assurance providers operate without the need for any specific professional qualifications, competencies or skills. Assurance providers have heterogeneous professional backgrounds and experiences that lead to substantial diversity in sustainability assurance quality levels. This paper aims to provide an understanding of sustainability assurance quality. From a legitimacy perspective, the authors focus on the choice of assurance providers by exploring why a company voluntarily chooses an incumbent financial auditor to jointly provide audit and sustainability assurance services. The authors argue that to avoid the legitimacy threats undermining stakeholders’ confidence in the sustainability information disclosed, companies should only choose their incumbent financial auditors to provide sustainability assurance services when these auditors possess the professional attributes associated with sustainability assurance quality.

Design/methodology/approach
This study develops regression models for an international sample for 2007–2016, where the authors analyze why a company voluntarily chooses an incumbent auditor to jointly provide audit and sustainability assurance services from a legitimacy theory perspective.

Findings
Evidence confirms that the choice of incumbent auditors as assurance providers is more likely when these providers are more specialized in the industry. The authors also find that independence does not play a significant role in this decision. Therefore, an assurance provider’s industry specialization can be understood as an attribute that is associated with sustainability assurance quality and one which limits the legitimacy threats caused by a lack of sufficient sustainability knowledge.

Practical implications
Given that companies have complete freedom when choosing their assurance providers, the selection of a high-quality incumbent auditor is an indirect measure of social commitment and a mechanism to improve public trust. The results confirm that it is fundamental for firms to understand the situations when choosing an incumbent financial auditor to provide sustainability assurance services is the best way to ensure firm legitimacy while obtaining higher sustainability assurance quality due to the spillover effect. This paper provides useful evidence for firms and managers who can become aware that the legitimacy threat associated with the auditing profession’s questionable competence to conduct efficient sustainability assurance engagements can be reduced if they hire an incumbent financial auditor with greater industry specialization. For assurance providers, the results are especially useful, as they should know that companies will be more likely to choose their incumbent financial auditor when that auditor possesses certain professional attributes, like industry specialization. The ability to assimilate and exploit the knowledge gained through auditing activities can be improved even more by specialization, which enhances sustainability assurance quality.

Social implications
From a social perspective, stakeholders perceive industry specialization as an indicator of the professional skills necessary to increase both the real and perceived quality of sustainability assurance services, thereby limiting the legitimacy threat arising from a lack of sustainability knowledge. The evidence also provides valuable results for regulatory bodies, as it shows that firms are not able to address the legitimacy gap caused by stakeholders’ perceptions that incumbent financial auditors can easily be controlled by companies. Thus, doubts arise as to whether this joint provision undermines auditor independence. Precisely, these doubts about assurance provider independence can erode public confidence in assurance and devalue the quality of the service. The results of this paper highlight the need to strengthen regulation on sustainability reporting and assurance. The advances and relevance of sustainable development in recent years and in future agendas require a firm commitment to sustainability reporting and assurance of quality, reliability, integrity and confidence.

Originality/value
First, this study contributes to recent empirical studies that focus on the role of sustainability assurance services in the legitimation process of corporate sustainability reporting. However, while that research analyzes how the legitimacy theory explains the voluntary adoption of sustainability assurance, this paper adds to the literature by presenting evidence about why certain incumbent auditors are appointed to carry out sustainability assurance services. Second, this paper contributes to the sustainability assurance quality literature. Third, unlike previous studies that have regressed various client-specific and institutional factors that influence firms’ decisions to choose assurance providers, this study contributes to the research by providing knowledge about a set of professional features that may explain the decision model of assurance providers selection from a legitimacy perspective.