Predatory publishers are exploitative and opportunistic publishers with the sole purpose to make money. Some red flags include:
Predatory publishers find scholars through various ways
Adapted from Shamseer et al. (2017). Potential predatory and legitimate biomedical journals: can you tell the difference? A cross-sectional comparison. BMC Medicine. 15:28. DOI: https://doi.org/10.1186/s12916-017-0785-9