What makes a source reliable? To determine whether a source is reliable or not you must look at certain criteria.
Accuracy is one of the four criteria.
Inaccurate information is useless to you, no matter what kind of research you're doing. Protect yourself from misinformation by:
Look for citations. Authors who cite their sources are giving you a pathway to the information that they used to write their article, web page, book, etc. You can track down those citations to be sure that the original source is accurately quoted or summarized.
Avoid using statistics or "facts" from a site that you suspect is biased. Learn how to spot bias here. An organization or individual that wants to persuade you is more likely to "massage" data to fit their own agenda.
Be a fact checker. Can you find any additional sources that corroborate a questionable fact, statistic or claim? If not, think twice about using it. Click here for fact-checking tips.
Stick with scholarly sources! These have quality-control measures in place and are far more likely to be accurate.