When we're talking about print sources, we can start by saying that supermarket tabloids do not generally count as reliable.
Magazines are generally less reliable than journals.
Periodicals are evaluated in Magazines for Libraries , a guide for librarians. With the Internet as with other sources, readers and researchers must take a critical approach toward information. The Internet, unfortunately, doesn't have a framework for reliability established yet. And since just about anyone with a phone line, modem, and computer can become a Web server, the opportunity for disseminating questionable information is high. Worse, if you've found the information through a Veronica search on Gopher, you may have no idea where the information came from and no sure way to tell someone else where to find it.