The argument, information, project, etc. on which you are working is only as strong as the evidence you bring to it.
Your writing or presentation takes on the character of your sources. If you use unreliable sources, your own paper will be unreliable and unbelievable.
To be believable to your reader(s), you must bring to your paper the opinions and research of experts. Such sources are written by the experts themselves or rely on expert opinion/research for their content.
Check your sources for:
Currency: the timeliness of the information
When was the information published? Has the information been revised or updated? Does your topic require current information, or will older sources work as well?
Relevance: the importance of the information for your needs
Does the information relate to what I want to know about? Is the information at an appropriate level (i.e. not too elementary or advanced for your needs)? Have you looked at a variety of sources before determining this is one you will use?
Authority: the source of the information
Who is the author/publisher/source/sponsor? What are the author's credentials or organizational affiliations? Is the author qualified to write on the topic? Is there contact information, such as a publisher or email address? Does the URL reveal anything about the author or source?
Accuracy: the reliability, truthfulness, and correctness of the information
Where does the information come from? Has the information been reviewed or refereed? Can you verify any of the information in another source? Does the language or tone seem unbiased and free of emotion? Are there spelling, grammar or typographical errors?
Purpose: the reason the information exists
What is the purpose of the information? Is it to inform, teach, sell, entertain or persuade? Do the authors/sponsors make their intentions or purpose clear? Is the information fact, opinion or propaganda?