Predatory publishing is a relatively recent phenomenon that seems to be exploiting some key features of the open access publishing model. It is sustained by collecting APCs [Author Processing Charges] that are far less than those found in presumably legitimate open access journals and which are not always apparent to authors prior to article submission.
Here's a recent article that will help answer this question:
Potential predatory and legitimate biomedical journals: can you tell the difference? A cross-sectional comparison
Take a look at Table 10 for a concise list of the features found in predatory journals, including:
- The scope of interest includes non-biomedical subjects alongside biomedical topics
- The website contains spelling and grammar errors
- Images are distorted/fuzzy, intended to look like something they are not, or are unauthorized
- The homepage language targets authors
- The contact email address is non-professional and non-journal affiliated (e.g., @gmail.com or @yahoo.com)
However, while perhaps not relevant to your immediate publishing decisions, please be aware of the Institutionalized Racism of Scholarly Publishing:
- Non-Western and/or non-English journals are hugely underrepresented in our current scholarly indexes
- The scholarly publishing infrastructure demands journals be Open and English to be noticed, but non-Western and/or non-English journals may be labeled as predatory as they struggle to fulfill such demands.