skepticism Or denialism Where's The Limit?

Where is the line where being skeptical about a specific topic becomes flat out denial? What is the methodology you use to filter through information to find the truth? How do you work through your bias towards information on topics you do not agree with & how much skepticism do you apply to information on topics you fully agree with? Most importantly can the film Scooby-Doo on Zombie Island help give us some perspective?