6. Conclusions
In the present paper, we have tackled the lack of research into the differences in audit fees between voluntary and mandatory audits. Based on the theory that prices have a signalling effect on credence goods, we argue that voluntarily audited companies may be charged with a premium, that is not charged for mandatory audits, in order to signal their commitment to accounting quality. Using a sample of Spanish SMEs, we empirically examine whether the pricing for voluntary audits is different to mandatory audits. We also examine whether the Big 4 premium observed in previous literature remains among SMEs, especially for voluntary audits. Furthermore, we consider the role of Middle-Tier auditors (Peel and Roberts, 2003; Clatworthy and Peel, 2007; Sundgren and Svanström, 2013). Although initially we did not find significant differences between voluntary and mandatory audits, the additional tests controlling for the comparability of firm size and using the PSM methodology showed that there is a premium for voluntary audits, which we associate with the signalling effect of prices on the quality of voluntary audits, in contrast to “passively compliant” companies which are required to be audited and choose “low-cost” audits regardless of their quality. With regard to large auditors, we find a Big 4 premium in both the voluntary and mandatory settings, while the premium associated with Middle-Tier auditors is not significant in the voluntary setting. These results suggest that, while Big 4 auditors may be concerned about the effect that different price policies can have on their audit quality reputation, Middle-Tier auditors are willing to follow a different competitive strategy for voluntary audits, in order to gain access to this market segment.