They have to be elected every five years. One of my best friends in the hobby is Mick Freeborn, who is a regular visitor to my birdroom and aviary. Yet last year he placed an excellent Grey Green cock of mine second in the class. I had high hopes for the bird, which were dashed. I don't know if he recognised the bird, but he placed it where he thought it deserved to be.
Judges are available for election each year, when clubs pick the next show's judges.
How long would a judge's reputation survive if he kept getting it wrong for whatever reason. The engagements would dry up. Judges are often accused of putting up well-known birds with a history of success. Yet how often are judges criticised if the bird which won last week, or two weeks ago, is beaten. Some birds always win, or at least are always in contention.