You have seen the general hierarchy of scientific literature and you learned of the difficult path a contribution must pass in order to enter the primary literature. You also learned that you could generally rely on primary literature, but that most peer reviewed journal articles focus on specific new research findings. These tend to be minutia and/or are not comprehensible to those outside of a narrow field. Here we will continue through the major classes of scientific literature.
Secondary literature
I use the term "secondary literature" to describe: Peer-reviewed review articles, lists and compendiums, and textbooks.
Peer-reviewed review articles. Often the editors of the primary literature recognize that so much has been published on a topic that it is no longer practical for an individual scientist familiar with a field to distinguish among the many articles. Sometimes topics are "hot." And some societies or commercial ventures devote an entire journal or one or two issues each year to publish reviews. The review author, usually there are several authors, are acknowledged experts in the field under review. The review article will attempt to summarize all the research on that topic, at least since the last review article. Review articles have hundreds or thousands of references. The review article itself will go through the same peer review process as an original article. Authors of the review article vary in their approach. Some will be opinionated and not report or report and belittle research they do not agree with. Other authors will feel obliged to report everything, including material they do not agree with. In general, you can rely on the information in a review articles.
Lists and compendiums. Many lists and compendiums are part of the regulations, here is a list of chemicals that the State of California treats as causing cancer. Cal List EPA. Other lists are put together by commercial and professional organizations. The ACGIH puts together a standard of workplace levels of contaminants, the TLV list. Many of these lists have references, that is, there is a citation that references where the numbers you are reading come from. Usually, when you need to use such lists, you can rely 100% that the number is on the list and the number is "123.4 mg/L". That is, you can correctly say, "Bromate -CAS-- 15541-45-4 is on the California List of Carcinogens." You generally have no way of knowing if the facts or numbers on the list are correct in the sense they describe some sort of reality. For example, for the vast majority of the chemicals on the California List, there is no scientific proof they cause cancer in humans.
Publishers of textbooks select authors based on the ability of their names to sell textbooks, at least initially. Then if a book sells well,the publisher will ask the author to revise it and update it. Many of the lists, tables, and figures in textbooks originally came from one of the sources above. Some textbooks quickly become out of date. Other textbooks are collections of chapters, each written by a different author. It is unlikely that a textbook author would be an expert in any but a few of the areas covered. In general, textbooks provide good background and have good explanations about how to do things, but are vague on the details you need in any particular situation. Paper textbooks usually have a nice index.
Tertiary literature
On top of the tertiary literature is gray literature, reports by consultants and experts. While the quality is highly variable, it is often the most pertinent to the particular problem you are working on. If you keep the bias of authors in mind, the data is often useful. My experience and intuition both indicate that moneyed interests don't want to publish anything that is untrue or incorrect. They might put a "spin" on the document or not publish an unfavorable finding at all, but what they do put out tends to be factually correct. The same is true with government reports.
Trade magazines are commercial ventures that live off advertising income. The articles in them are often written by professional writers and tend to be the most "readable" of the literature sources. Often there is no one in the magazine office who has the technical expertise to critically read the articles that they print. While the English is usually correct, there are often typographical errors in tables and formulae.
Popular literature
At the far end of the reliability scale are newspapers, magazines, and TV. It is rare that anyone in the data transmission process understands any of the technical details about what they are reporting on. Some have a "science editor" who has a degree in something other than English literature, but they are unlikely to be experts in any particular thing. What the media often do, to give their science reporting some creditability, is interview "experts." These experts are usually chosen for their contributions to the controversy surrounding the matter, rather than scientific expertise. We will talk more about public involvement later.