Our e-mail inboxes are overflowing with invitation to publish here and there. Some of the invitations are legitimate and some are not. These gray publishers are there to charge the article processing charge APC – a charge that the author pays to get published in the journals. PLoS, Public Library of Science uses this model to finance the mega journal but this does not make PLoS a gray publisher. A gray publisher is one that does not have very high standards and is e.g. lacking proper peer review.
It is not only these gray publishers you should be aware of. There are even gray conference organizers. One example i OMICS. In the blog Scholarly Open Access a post was published where a scientist is giving an account of his experiences of the conference organized by OMICS. In short: the conference was not organized, it was shortened by one day (from three days to two) without any prior announcement, a number of presentatitons were not given and since the conferense in reality only lasted a day and a half many of those attending the poster sessions could not take part.
If you are suspicious of an invitation to publish or to take part in an conference, contact me so we can together discuss the invitation.