The New York Times has an article, Scientific Articles Accepted (Personal Checks, Too), about what one journal editor calls “the dark side of open access.” Some legitimate open access journals charge a fee to authors publishing articles in their journals. (That’s how they make it free to you, the reader.)
However, there seem to be some journals that will publish anything as long as they get paid. (In the old days, this was known as vanity publishing.) Sometimes, apparently, academics are tricked into publishing in these journals, or they are falsely listed as being on their editorial boards. A related phenomenon — and one I hadn’t known about — is fake conferences, in which academics are charged to give presentations.
The NYT has a nice explication of all of this for laypeople, including a link to University of Colorado librarian Jeffrey Beall’s blacklist of potential, possible, or probably predatory scholarly open-access journals. There are some useful comments following the article, too, though I admit I did not read all 300+ of them.