What is the most precise form of turbinate reduction?

It totally depends on what "issues" your hypothetical person is still having.  I would be hesitant to ever perform revision turbinate reduction on most patients.  It depends on what was done last time and a host of other factors.  I usually think that if turbinate reduction did not work once, then it will not work again.  It is more likely that septal deviation, allergic rhinitis, nasal valve obstruction, etc.  are the cause of residual breathing obstruction.  To answer your question, I would say the most precise way to reduce turbinates is the use of a microdebrider designed to perform conservative submucosal reduction of turbinate tissue without harming the overlying mucosa.  Gently outfracturing the turbinate is frequently done as well, which I would consider safe.  I do not like the term "turbinectomy" because, except under extreme circumstances, the turbinates should never be resected (or partially resected).  They perform a vital function for the nose and have to be treated as such.