My clue for identifying a Single Best Thing is when my light bulb comes on.  It captures my attention and I have that "ah ha" moment.  Their strongest referral opportunity lives in the moment of the presentation when the member clearly solves a very specific problem for a very specific person. 

Like when Wayne Thompson was able to help a client who was graduating from Med School and he was able to get them approved for their new home with a loan created for thelr profession and based on their offer letter for employment.  That immediately stood out to me and I remember the situation not just the service.

That makes it easier for me to recognize referral opportunities later because I’m listening for the problem they solve, not just their title.