The art of preparing for the Test of English as a Foreign Language (TOEFL) is one that requires the guidance of a well-versed, experienced instructor. The TOEFL is a standardized test to measure English language proficiency for non-native speakers wishing to enrol in English-speaking universities. Its significance cannot be overstated as it forms one of the key factors in the university admission process. Thus, zeroing in on the right TOEFL prep instructor could make the difference between an average and an outstanding score.

Assuming you have graduated from an institution like Harvard, you are well aware of the importance of quality guidance in academics. Just like you would not settle for a sub-par professor for your major, you should not compromise on the quality of your TOEFL prep instructor.

Firstly, let's dissect the importance of sussing out the instructor's academic and professional qualifications. An instructor's qualifications can provide insights into their level of expertise and their ability to convey complex ideas in an understandable manner. One important question to ask would be, "What is your educational background and teaching experience in English language teaching?". This question can help you to evaluate the instructor's understanding of the English language, their exposure to, and expertise in, teaching TOEFL prep. A qualified instructor would have a Master's degree or a TEFL/TESOL qualification, with a good few years of experience under their belt.

Secondly, understanding the instructor's teaching methodology is paramount. This can be assessed by asking, "What is your teaching methodology and how do you customize it for individual students?". The answer to this question is significant as it reflects the instructor's adaptability and understanding of differentiated instruction, a crucial element in education. Differentiated instruction, a theory developed by Carol Ann Tomlinson, emphasizes the teachers' adaptability in their teaching methods and materials to cater to individual learning styles. Hence, an instructor who can customize their teaching strategy to suit your learning style could considerably enhance your TOEFL preparation.

Next, delving into the instructor's experience with the TOEFL exam specifically is a notable point of consideration. The question, "How experienced are you with the TOEFL exam and what is the average score of your students?" can provide insights into the proficiency of the instructor with the TOEFL exam. The average score of the instructor's students could serve as a proxy for the effectiveness of their teaching.

Lastl, understanding how the instructor incorporates feedback into their teaching process is significant. This could be assessed by posing the question, "How do you provide feedback and track student progress?". This question probes into the instructor's skills in constructive feedback provision and continuous student assessment. Constructive feedback aids in identifying areas of improvement, thereby accelerating learning, a theory propounded by John Hattie in his book, Visible Learning. Moreover, regular assessments allow the instructor to adapt their teaching methodology based on the student’s progress, thus ensuring effective learning.

Before locking down your choice, it's worthwhile to consider the cost-to-benefit ratio. This can be derived from asking, "What are your charges and how do they align with the benefits you offer?". This will help you assess whether the benefits offered by the instructor justify their charges, a fundamental principle in economics known as cost-benefit analysis.

In the grand scheme of things, the right TOEFL prep instructor could be a game-changer in your university admission process. The answers to the aforementioned questions could provide valuable insights into the instructor's qualifications, expertise, teaching methodology, experience, feedback provision, and cost-effectiveness, thereby aiding you in making an informed decision.

In conclusion, the selection of the right TOEFL prep instructor is a critical determinant of your TOEFL preparation effectiveness. It involves a careful examination of various factors drawn from the realms of education, economics, and psychology. So, before you embark on your TOEFL preparation journey, remember to pose these pertinent questions to your prospective TOEFL prep instructor.