What is transfer pricing?

For the first on campus interview: I was not asked too many technical questions about transfer pricing methods or calculating a TP price with a specific method from financial statements, etc. Interviewing many times this semester for TP positions in particular has made me well versed in these interviews, especially at the intern level where my experience has been that they don't expect applicants to have much knowledge on the subject yet. Mostly they just asked me about what I thought my strengths were compared to other candidates and why I was interested in transfer pricing. Then they asked me what my quantitative, accounting, or econ background was. Other than that it was behavioral getting to know me and then answering my questions at length that I had for them about Duff & Phelps and their transfer pricing practice (formerly CETERIS). I think knowing what questions to ask that let them highlight the differences between Duff and other big 4 firms and other questions that showed I already had some knowledge of what transfer pricing looks like in practice is what made them refer me to a specific location and an internship opportunity. For the second (first round screening) interview with a director, it was again mostly behavioral questions and why my interest in TP and a few things from my resume. Fairly straight forward. However, my peer interviewed with another Duff & Phelps office for a full time transfer pricing analyst position and said the first phone interview was much more technical with questions about which financial statement do you think is the most beneficial for TP and why? (Income statement, because TP prices for RPM, Cost +, etc can be calculated directly from it). Also question about what is the best TP method (one that gives the most reliable arms length result, usually a direct CUP [if available]but if not judgment and experience will help decide which of the other methods is best for that transaction). In my case, the final interview was just another behavioral with very easy and discussion based questions off my resume or my background and interest in the field again. I was more nervous beforehand expecting it to be tougher knowing it was the second round but that conversation actually felt the most natural and slightly less formal than the others as I was speaking to someone close to my own age. I could be wrong but my guess is that this interview was to give their associate experience interviewing and to see if this associate thought I communicated effectively and was pleasant enough to work alongside as I would probably be mentored by as I assist in doing similar tasks.