First, employers want to be sure they are hiring candidates who came from real, certified schools. Additionally, if a student chooses to go forward into graduate school, some colleges will turn down their admission due to lack of proper credit if they did not attend an accredited school. This can cause major headaches, as students may end up being forced to take and pay for classes already taken before in undergraduate school.
Since accreditation is very important, most schools, if not all who are really accredited will be sure to list this on their documentation. If you aren't sure a school is accredited, ask someone beforehand and ask to see some credentials in writing. Most schools will have this information readily available to students so they can be sure they're attending an accredited school. Check with the proper government agencies or the NEA to be sure. It is often much easier for online universities to state they're fully accredited when they aren't, because their students are not physically on campus.
Faking accreditation is particularly easy for online, or distance learning schools. The first thing to look for is the school's contact information. There should be more than just an email address or fields to send in comments and questions. Accredited schools should list a directory with actual names and telephone numbers. Keep in mind, just because a school's website looks nice and is well done, does not mean the school itself is legitimate. It is all too easy today to create a professional looking website that hides behind the facade of an imposter. Use your gut instincts.
Sources: Distance Learning at About.com Degree Info Tutorials