Update 2020-01-24: Beall’s list has a new home: https://beallslist.net/
With your academic email address posted online, you’ll be flooded with sketchy offers inviting you to submit your manuscript to open-access journals with legitimate sounding names like “British Journal of Science” or “Cancer Research Frontiers”. These predatory journals typically do little or no peer review. One pair of scientists was even able to get a paper containing only the repeated text “Get me off your f___ing mailing list” published in the predatory International Journal of Advanced Computer Technology.
The proliferation of these journals is perhaps the chief disadvantage of the move towards open access since, in the digital age, setting up a website is nearly free, and open access journals need not convince any librarians to pay for subscriptions to make money. Instead these ‘journals’ charge huge fees to publish and conduct shoddy peer review or none at all. Some are less directly predatory, but are instead “vanity press” where they get you to pay a fee to publish your thesis with them with little editing or review.
You might also find yourself invited by [person you’ve never met/heard of] to give a talk at [prestigious conference you’ve never heard of] organized by [not a university or professional society]. When you go to register, you’ll find that it’s bizarrely expensive. I think that at least sometimes conferences are real, but like the predatory journals, they are just doing it for a profit.
At least in the case of the predatory journals, Beall’s List of Predatory Journals and Publishers (now located here)provides a great way to check if the journal is a known scam so you can end that email to your spam folder without a tinge of fear that you’re throwing away a legitimate offer. Two notes of caution here: (1) obviously just because it isn’t on the list doesn’t mean everything is above board, so still do your due diligence and (2) on the Beall’s List, you have to click through publishers, standalone journals and vanity press and search each separately.