Purpose - This study aims to employ the Model of Goal-Directed Behaviour (MGB) to examine the consumer acceptance of technology-based self-service (TBSS) for a credence service instrumental to a social goal. Credence services are increasingly delivered via self-service technology and in social marketing, the achievement of social goals can be contingent on consumer acceptance of these services. However, little is known about the determinants of acceptance and extant marketing literature fails to account for emotional and goal influences which are likely to be important. Design/methodology/approach - The authors interviewed 30 young adults with self-reported stress, anxiety or depression as potential users of a self-help mental health service delivered via mobile phone. The data were analysed deductively and inductively with the assistance of NVivo. Findings - The findings generally support using the MGB to enhance understanding of consumers' acceptance of TBSS. The paper also found evidence of the importance of maintenance self-efficacy, the self-evaluation of the ability to continue using the service, and a previously ignored element of consumer level competition that arises between alternatives that achieve the same goal. Originality/value - This study is the first to examine factors that influence consumers' acceptance of TBSS for credence services aimed at achieving a social goal. It builds on understanding of consumer decision making in social marketing, particularly the influence of self-efficacy and competition. It also contributes to attitudinal research by providing initial evidence for deepening and broadening the MGB in the context of TBSSs.