One symptom is if someone understands and accepts that this world is temporary will take to the message of Krishna in earnest. What I mean is when we internally accept the message of temporariness, then all so called problems of this world will come into focus more clearly. It will also help us to gradually give up our attachments of this world.
Another symptom of someone who will take to the message of the Gita is the fact that we are spiritual beings encased within a physical body. This also will help put things into focus as far as this world is concerned. This also will impact the way we live our daily lives as parents, student, employees, friends etc
If we study the Gita, we will find that Krishna also begins His message by speaking about these two crucial points. (1) we are spiritual beings (2) this world is temporary and that we should simply perform our duty without being disturbed.
These two points can be used as a way to assess if someone will take to Krishna Consciousness or not!