With the advancement of robotics technology, humans will increasingly interact with multiple service robots, yet there are still gaps in understanding how the behavior and appearance of the service robots can impact the interaction. Our two-stage study focuses on human interaction with two librarian robots. Specifically, we examine how the perception of robots as “authoritative” or “service-oriented” affects the quality of interaction. First, we conducted an online study with 140 respondents to define the look and behavior of authoritative and service-oriented robots. Based on this, we developed the behavior and look of the robots and executed a real experiment with two robots in a library setting. Outcomes obtained from 20 participants indicate that they preferred an authoritative behavior and a service-oriented appearance for optimal task success and better interaction quality.