At the judges briefings for the shows I've judged I've been told to remain impartial, to not comment on the cars I was judging so as to not appear to be impartial, to not touch the car, to not discuss the relative merit I put on any one car over another, to, as it was put, be mute. And no smirking, no tsk-tsk-ing, no facial or visual cues either to indicate opinion.
At some malt-shoppe impromptu gathering it might be fine for the judges to offer their opinion, but that was not permitted at the level of the shows I was asked to judge. No, not Pebble Beach level, but the entrants and the staff were taking just as seriously. Once I witnessed too seriously when a judge muttered, loud enough that I also heard, "Now that's just stupid" and the car's owner took offense and then took offensive action.
That comment that day went far beyond constructive criticism, but at what point does criticism become a "dope slap"? Easy enough to avoid that entirely with silent, emotionless judges.
And the judges, as well as entrants, always knew who trailered in, who trailered to within 5 miles to pretend that they drove, and who had the daily drivers that almost invariably won over the queens.