Jury trials allows others to reviewed by their peers and have more than just one person dictating if the person in question is guilty or not. They are pretty effective and help get better accuracy because it is several people all taking the facts and talking it out with one another.
Jury trials are an effective means to achieving justice when the selection process is done in a fair way. Juries that contain significantly more of one sex than the other, are selected in favor of one race or nationality, or overwhelmingly comprised of individuals who are overly conservative or overly liberal bring the jury system into question. A random selection process, however, that ultimately results in a balanced jury is a good means to achieve justice.
Regular people don't have equal means at their disposal, and richer people almost always have significantly more resources. More resources results in a better defense than not having a lot of money like the "poor class".
Also, judges could be paid as richer people have extremely more contacts with private detectives and expert witnesses. The jury will be biased as more proof is directed towards the side with more lawyers, more defense.
Finally, more money equals more lawyers to hire, and the more money you can pay, the better the lawyer you can get. More money can hire the best lawyers the government can offer you.
People are often unaware of their own psychological biases and fail to account for them. People will say they know "beyond a reasonable doubt" off of overconfident estimations of facial expressions and body language even when a scientific look would say there could be many reasons why.
Juror should be a professional job requiring a degree involving among other things classes on reading facial expressions and body language that emphasize how people are often overconfident and there tend to be many explanations for these things.