You should always greet people.
Sarah is in an office building waiting for a job interview and Amanda enters the room.
Sarah wants to finish waiting and get to the interview quickly.
Sarah greets Amanda and wishes her good luck on her interview.
Sarah ignores Amanda as she enters the room and says nothing.
Amanda replies thank you, but also that she's the interviewer, not a candidate.
Sarah is called into the interview 10 minutes later and Amanda is the person interviewing her.