Why am I a credible source? Probably because there is no one that could tell you more about being an R.A. than an actual R.A.. Other than that, I expect to reference common incidences as well as wild ones, the more general of incidences are things that regular students can relate to (or have experienced themselves) which will make them trust me as a source. Once you can identify with a couple things someone is saying, you usually find yourself trusting the rest of their claims.
Since my intended audience is college students, another reason my they will trust me is because we are peers. The natural inclination of students is to take a professor's knowledge at face value in class, completely disregard it outside of class, and forget both in no time. But with peers there isn't such harsh rules, usually the code is "true until proven false", so I don't expect credibility but I will most likely give it.
Lastly, who in college even notices credibility? Um hi, Wikipedia is the life's blood of 80 percent of papers written here at URI. I think I'm good.