A common misconception about OA is that it entails anyone being able to post anything they want to the Internet. In reality, scholarly OA journals function on peer review models that mirror the variety and rigor of traditional print journals. The "open" refers to the free availability of research to the public, not to the removal of the review process that has been the basis of scholarly publishing for three centuries. Open access is in every way compatible with rigorous peer review.
What is key to know is that so-called "predatory" publishing has existed for long before open access. However, because open access is becoming the dominant model for all new journals, predatory publishers are following that trend as well.
When people say "predatory" in relation to publishers, they generally mean journals deliberately taking advantage of academics by publishing their work without providing any of the actual vetting and quality control expected of academic writing. They may provide the veneer of doing these things in their advertising and web presence in order to mislead authors. In practice, it may be difficult to distinguish a predatory journal from one that is just new and emerging. In addition, some very established publishers with well-respected journals may have practices that could be described as "predatory."
What follows are some signs ranging from strong negative indicators (i.e., those that indicate likely predatory behavior) to other negative indicators that may indicate problematic issues with the journal whether it is predatory or not.
The following should be taken as signs to treat a journal or publisher with significant suspicion of being a predatory journal:
The following may suggest reasons to be suspicious, although they can be true of non-predatory journals, even good ones.
These problems are often seen even in specific journals by large publishers that are otherwise reputable and may have other journals that have very strong practices. You will likely want to avoid these regardless of the publisher reputation.
Not every good journal in the field will have these things, but they are positive signs: