Here's a quick guide to whether a book review is usable:
- Selectivity: The more selective an outlet is, the more likely it's going to be reliable. However keep in mind that this isn't always a foolproof way to detect unreliability, as there are outlets who put out a seemingly large amount of reviews that are reliable. For example, the Horn Book Guide puts out a large amount of reviews but is also fairly selective in which books they review for their publication. Publisher's Weekly also puts out a lot of reviews, however they're also relatively selective as well.
- Ratings: If an outlet openly advertises that they only put out favorable reviews, then that's a strong sign that they're not reliable. It's rare that an outlet will make this claim and still be seen as reliable, as this puts into question whether or not they're just a praise generator.
- Fees: If an outlet charges for reviews or a fee for "expedited" reviews, then it's almost certainly not reliable. Outlets that charge and are reliable are going to be fairly rare. I think that the only one I've seen that would be usable is Publisher's Weekly, as their pay to review setup is separate from their main site and review outlet. Outlets like Reader's Favorite that offer "free" reviews but also charge for "expedited" reviews are definitely unusable, especially as they're known for only churning out praise.
- However keep in mind that allowing people to submit books for review isn't the same thing as the fee setup. It's fairly common for most outlets to have a page detailing their submission guidelines, as sometimes it's made visible as a way of preventing people from sending unwanted works. Using Publisher's Weekly as an example again, the main publication only accepts books via publishers and publicists.
- Reputation: This seems fairly obvious, but it's always worth mentioning. If an outlet is known for putting out quality work, then it's likely reliable. Has the outlet or its writers/editors won major, notable awards for their work for the publication? Does it have a very large reputation for misinformation? Is it routinely used as a RS by other RS, especially academic and scholarly sources?
- The New York Times would be an example of an outlet that has a good reputation and would be seen as a reliable source, whereas the New York Post is a tabloid known for their controversies over misinformation.
- Self-published: If an outlet is self-published then it's likely not reliable unless we can show where it's routinely seen as a RS by other RS. This comes particularly into play when it comes to indie and niche genre books, particularly in the YA genre, since a search is more likely to bring up blog reviews and coverage. I'm putting this separate from reputation since a SPS might have a decent reputation among its readers but still not be seen as a RS on Wikipedia.
- Independence/Secondary: If an outlet has a tie to the author or publisher, then it's going to be seen as a primary source. This doesn't mean that it can't be used in the article, just that it's likely not going to be able to establish notability.