Thats true but its the defense counsel that gets to thumbs up or thumbs down those called up for jury duty on the day. They can only pick from those present but you can be reasonably certain that those whose demeanor suggests someone who is reasonably intelligent or educated won't be selected. When I was called up for jury duty for a Supreme Court case I asked the judge to be excused as my aviation medical was due and not completing it in time would affect my income. I did get to see the selection process and it seemed that the men chosen had the look and demeanor of a tradie.