“These are OA journals that exist for the sole purpose of profit, not the dissemination of high-quality research findings and furtherance of knowledge. These predators generate profits by charging author fees, also known as article processing charges (APCs), that far exceed the cost of running their low-quality, fly-by-night operations. Charging a fee is not itself a marker of a predatory publisher: many reputable OA journals use APCs to cover costs, especially in fields where research is often funded by grants. (Many subscription-based journals also charge authors fees, sometimes per page or illustration.) However, predatory journals are primarily fee-collecting operations—they exist for that purpose and only incidentally publish articles, generally without rigorous peer review, despite claims to the contrary.”

Source: Berger M, Cirasella J. Beyond Beall’s List. Coll Res Libr News. 2015;76(3):132-135.

"Predatory publishers predate OA, their recent explosion was expedited by the emergence and success of fee-charging OA journals". http://blogs.lse.ac.uk/impactofsocialsciences/2015/03/18/beyond-bealls-list-predatory-publishers/

Watch out for predatory conferences as well !

1. Check the Websites for the standards they follow?
2. Does the Website look authentic and professional?
3. Are they open and transparent about any fees they charge?
4. Is the Journal indexed?
5. Is the Journal Peer Reviewed?
6. Is the Editorial Board authentic? Contact them !
7. Check previous articles that have been published, are they of sufficient quality?

As in the case of predatory publishers you may also receive unsolicited emails asking you to present/chair at conferences. If you are suspicious you may need to investigate it in the same way you would a Journal.  Check with colleagues, see if there were previous conferences, who hosted them?, who spoke at them?, what is the process for acceptance?, are the proceedings published? and if so where? are they contactable?

There are some tools available that rank conferences that you could use such as:

Sign up for academic mail lists in your relevant subject area and you will often be notified of up and coming conferences in your field. For example jiscmail https://www.jiscmail.ac.uk/ which helps groups of individuals to communicate & discuss education/research interests using email discussion lists.