One could characterize it as "manipulation," which has a negative connotation, but it could also be conceptualized as dealing with a person who brings something to the table—that is, who understands that your time / effort is presumably valuable, and that they shouldn't expect something for nothing. Trying to pay outright would be overly expensive and too intrusive, but a small thing like coffee demonstrates that the person wants to differentiate themselves from most people, and that they have something at stake.
People treat "free" as very different than "not free," which Dan Ariely describes in Predictably Irrational, and people treat exchanges in a special way, as Lewis Hyde describes in The Gift: Creativity and the Artist in the Modern World.
Manipulation: gift + nothing meaningful to share
Kind gesture: gift + something really meaningful to network about