Both types of reviews are valid.
Both types of reviews are useful to readers.
Different CriteriaProfessional reviewers use standards, similar to the way a teacher grades a test. They’re looking at things such as plot structure and use of literary devices. Readers tend to rate books based on their experience while reading. For example, if the book was a mystery readers might base their ratings on the cleverness of the puzzle to be solved. A romance book may be valued for the intensity of the love scenes, and plot flaws may be ignored if they contribute to making those love scenes happen.
These different sets of criteria are why the two groups often disagree in their ratings of the same book. In fact, I’ve seen a number of cases where a professional reviewer praised the use of a literary device and the general audience criticized the piece of work for the same technique (finding repetition boring and annoying, for example). I like to think of professional reviewers as examining the architecture of the book, while typical readers tend to rate a book based on how the story made them feel.
As far as books are concerned, there’s the integrity of the piece as a work of art, and then there’s the appeal of the book to the audience. The paradox is that critical acclaim and mass appeal often don’t go together in publishing. The horror film genre is a classic example of this dichotomy between critics and audience. Film critics tend to give low ratings to most of the movies in this genre. If you’ve ever watched one of these films, you understand why: the plots tend to be poorly constructed and unbelievable. Horror fans, however, know this about the films, but they’re going to see them for the rush they feel during the experience. Horror fans frequently ignore critics altogether.
So, Who Should Readers Listen To?The first step in overcoming this discrepancy between critical and reader reviews is to acknowledge that it exists. There may be times that you agree with the critics, other times that your opinion agrees with the pubic, and there will also be those few times when the critics and public both agree.
Next, treat information from both types of reviewers in the same way. They're both reviewers, they just have different sets of criteria. Therefore, I often advise people to find one or two of their favorite books and see if a reviewer has read them. If the reviewer hasn't read them, then it’s fairly safe to assume that the person has different taste in literature and this isn’t a reviewer who would have valuable input for you. However, if the reviewer has read the book, check to see if their opinion agrees with yours. If it does, then chances are you will agree on new books, as well. If the opinion differs, then look for other reviewers and see what those people have to say about the book. Eventually you will find someone else who has taste similar enough to yours that you can trust their judgement. You may also find a few who have such different taste from yours that when they like a book you know you'll hate it.
In the end, the average person is looking for a book to enjoy. Both professional and reader reviews can help you to find one. In fact, the best books often have the critics and audience in agreement on how good they are. But when critics and other reviewers disagree, find the people who have similar taste to yours on other titles and trust their judgements.