In 2006, as part of my clinical psychology doctoral thesis, I sought to examine predictors of outcome in psychological treatment; however, I was unable to identify an operationalized definition of a key term from which I needed to base my research. “Socialization to the model” was a phrase used ubiquitously in clinical textbooks; however, the definition differed and was too nebulous to test. It was essential to the success of my research that I adopt a rigorous approach and ask the question: what do people mean what they use the term “socialization to the model,” and more importantly, do they mean the same thing? The answers to these questions would allow me to test an essential ingredient in the therapeutic process. In this case study, I describe and critically appraise a methodology which allowed me to systematically obtain opinions of experts to produce a robust and statistically reliable definition of the term which was set to underpin my future research: the Delphi method. I discuss the advantages of the mixed-methods approach which offers flexibility from a number of perspectives, an advantage which deserves a cautious appreciation. I examine the inherent challenges of the approach, specifically the avenues for bias and highlight the essential role of the sample, drawing on my own reflections and experiences.