What is a Predatory Publisher? Publishers that exist mostly in the scholarly open-access environment who charge publication fees to authors without the providing editorial/peer-reviewer services that are common in legitimate scholarly journals.
Checklist:
(2017) Publisher Package and Open Access Journals: Are Any of Them Predatory?, The Serials Librarian, 73:3-4, 248-268, DOI: 10.1080/0361526X.2017.1389796
Clark, A. M. and Thompson, D. R. (2017), Five (bad) reasons to publish your research in predatory journals. J Adv Nurs, 73: 2499-2501. DOI:10.1111/jan.13090
Nerissa Nelson & Jennifer Huffman (2015) Predatory Journals in Library Databases: How Much Should We Worry?, The Serials Librarian, 69:2, 169-192, DOI: 10.1080/0361526X.2015.1080782
This video by Jeffrey Beall (University of Colorado Denver) gives an overview of predatory publishing.