Warning signs may include but not limited to:
Web of Science does not depend on the Journal Impact Factor alone in assessing the usefulness of a journal, and neither should anyone else. The Journal Impact Factor should not be used without careful attention to the many phenomena that influence citation rates – for example the average number of references cited in the average article. The Journal Impact Factor should be used with informed peer review. In the case of academic evaluation for tenure, it is sometimes inappropriate to use the impact of the source journal to estimate the expected frequency of a recently published article. Again, the Journal Impact Factor should be used with informed peer review. Citation frequencies for individual articles are quite varied. Journal Citation Reports now includes more article-level data to provide a clearer understanding of the reciprocal relationship between the article and the journal. This level of transparency allows you to not only see the data, but also see through the data to a more nuanced consideration of journal value.
Source: Journal Impact Factor - Journal Citation Reports - Web of Science Group (clarivate.com)