Actually you do not.
However there are likely to be recommendations coming out of the audit or analysis which may be difficult to implement if you do not believe that it will work.
These can be relatively simple to achieve ones such as placing a water feature in a certain sector, repainting the study room or to refrain from carry out renovation work in a certain sectors. Or much more difficult ones to achieve such as changing the location and orientation of the main door, changing bedroom and stove direction.
Or very much more difficult to achieve recommendations such as moving to another house with a favourable facing direction and surrounding landforms or asking your parents to come stay with you!
So the answer again is no, you do not need to believe. But if you do not believe then it is likely you will agree to the recommendations.
It is like if you do not believe that you can climb the mountain, the you will likely not make any attempts.