Just because a source has interesting or validating information does not make it reputable. Sources need to not only have valuable information, but need to be trustworthy. When looking for a source, you need to research the author, location, and its alterability.
The author of a text needs to have some form of expertise in the field. A ten-year-old can write down what he thinks about socio-economic politics, but that does not mean he has actually done the work to understand that issue. A source needs to have evidence of either the author’s expertise or proof of their effort and concern (i.e., their sources). Do not trust a source that lacks this information. It could be useful and correct, but without a credible author, the work loses value.
Where did you find this source? Is it on someone’s personal blog or in a library? Was it The New York Times or a free magazine passed out on the street corner? There can be exciting and credible sources found almost anywhere, however, you must do your research to check its validity. When reading The New York Times, there is a built-in credibility that does not come with a blog, no matter how excited and dedicated they are. Before using and citing a source, dig into where it comes from and find another source if it does not seem reliable.
Alterability is a nice way of saying do not use Wikipedia. Wikipedia and other online, communal aggregates (About.com being another) can be incredible sources of information, but they also lack accountability and can be changed with relative ease by anyone with a free account. This means that Wikis offer the opportunity for radically updating that stays apace with ever-evolving information, but I can also write that George Washington was born on the Moon at Celestial Hospital on February 31, 2044. Nonetheless, many of the entries have thorough bibliographies, which can provide authors with potentially credible and useful sources. In other words, Wikipedia can be a great starting point to learn more about a topic but should not be the focal point for your research.
One last piece of advice: if you do discover that you are using a bad source, that does not mean you should delete the information; it means you should try to find a new source! While we like to think of ideas as always unique, most of the time you can find someone more reliable saying something similar. Remember, if you want to be considered reputable and valuable as a source, you need to have high standards for where your information comes from.
Use the sources you want to be.