Scholarly books (or monographs) undergo a process of review, often by an editorial team or editor. They have been evaluated by one or more specialists before publication. These titles are often published by university presses (University of North Carolina Press), scholarly associations (Royal Society of Chemistry), but include other reputable presses/publishers/imprints (Wiley-Blackwell, Routledge). Like scholarly articles, scholarly books will include citations and be written by experts in the field of study.
If you are unsure is a press or organization is academic, you can search for the name e.g. Ashgate with the word about. You may have to add the word publisher or publishing.