The study investigated how novice supervisors in postgraduate family medicine training in Saudi Arabia make decisions about trust towards trainees. In 2022–2023, they conducted semi-structured interviews with 20 supervisors with less than 5 years of supervisory experience and analyzed the data using a framework approach according to the trust formation model. Supervisors see trust as a gradual process influenced by cumulative observations, clinical risk and responsibility. Initial interactions involve high surveillance and low trust, which increases with repeated exposure and relationship building. Institutional barriers such as short rotations, legal constraints and high workloads prevent the development of trust and lead to superficial or false credentialing. Supervisors with more clinical experience are more confident in establishing trust, while less experienced ones rely on careful checklists. Faculty development programs, structural support, and longer rotations can improve confidence calibration.