1) He is regarded as a Gadol b’Torah by the Gedolim already established as such.
This means that they give serious weight to his opinion in their own Halachic rulings.
2) His Torah is studied widely in Yeshivos and Kollelim
3) Community Rebbeim (of various communities) turn to this person with their own shailos
There have been many known tzaddikim who did not meet all of those criteria.