What behaviors show empathy during a one-to-one business interaction?

That's not what behavorial psychology means. Behavorial psychology
involves operant conditioning - treating symptoms rather than analysis
- what Dr. Phil does most of the time.

Empathy can be shown by using eye contact, an interested expression
and good listening skills. Ocassional feedback to let th eother person
know you understand what they are on about. eg repeating what they
have said like "so you use the banana as a telephone when you are
stressed" and " I see" or "ah ha" with appropriate nodding. Facing the
other person with your hands on your knees and bend a little from the
waist. These things will all 'show' the other person that you are
'actively' listening to them, and understanding them and these things
build empathy.

fishgirl5 is right, it sounds suspiciously like you would do on a date
(and it is) I just didn't want anyone to go off on the wrong tangent
searching for this in the wrong areas - Skinner would never forgive me
(GRIN).