These tests can include physical exam and blood or urine tests performed by a medical laboratory. Hair, eye and muscle strength tests are bogus and cannot determine nutritional status of any vitamin or mineral. Ask what their tests prove or disprove, how they remedy deficiencies noted on their tests and the research supporting their treatment recommendations. Nutrition practice is based on research that has passed the rigors of multiple research studies and review by other scientists. Ask about the research behind their diet or supplement.
Most nutritional remedies take time to take effect, especially weight loss.
Ask what you are supposed to eat when you go off their products and if your nutritional deficiency or lost weight will return. What is natural about a pill unless you have seen a pill tree, bush or plant. The human body has evolved over thousands of years eating whole foods, not supplements. Ask them what the difference in similar supplements between their products and brand name synthetics. There are positive and negative aspects to every food and supplement.