The defence is only entitled to six peremptory challenges so trying to wean out a particular category of prospective juror based on looks alone in the 10 or so seconds that defence counsel has between them being called forward and them starting their oath or affirmation is a bit of a stretch
So you dont think the defense counsel is not checking out the potential jurors in the 15-20 minutes of the Judges preamble prior to jury selection? If you go for a job interview you have won or lost the job in the first 30 seconds of being in the room. The selection panel will have formed an opinion that will be reinforced by your subsequent performance.