We have to be very careful about the credibility of the information that we are gathering. Also, as with any information, we have to think about the biases that might be inherent in the writing. For example, if we are writing about animal rights, then obviously PETA will be a biased source. This doesn't make it an unusable source, we just have to handle it accordingly because of the built in bias.
What are some of the biases that show up in advertisements?