Affinity bias often shows up as a feeling of easy rapport. An interviewer who went to the same university, supports the same team or shares a way of speaking may rate that candidate higher on communication or fit without any job-relevant evidence. It also affects which CVs get a second look, since a familiar employer name or hobby can catch the eye while equally strong profiles are passed over.
Left unchecked, it narrows teams towards people who resemble those already there, and it is hard to spot because it feels like good judgement. Asking every candidate the same questions, scoring answers against written criteria before discussing them and involving more than one assessor all reduce its pull. Recording the evidence behind each rating shows when a score rests on likeability rather than ability.