Predatory publishers and journals target researchers with "too good to be true" offers, prioritize profit over quality scholarship, and lack proper vetting and peer review. Researchers who publish in these venues risk damaging their reputations and credibility in their fields.
Red flags to look out for:
The most important thing to keep in mind is that legitimate journals can publish legitimate research that may have some of these red flags; if you spot only one or two of these things, you don’t need to automatically dismiss the journal/publisher as predatory. But the more red flags you see, the more likely it is that you are dealing with a predatory publisher.