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It is generally not useful or productive to doubt the correctness of the content you are consuming, be it content for learners, content for native speakers, or content that's been translated or dubbed. Particularly in content that's not scripted, native speakers misspeak every now and then. But children acquire their language well even though the adults they listen to sometimes make mistakes. They listen to a lot of language and most of the time it's correct. And since acquiring a language is a gradual process, they don't learn those mistakes. Like children, the way we acquire language as adults is with extensive listening and reading. When you receive large amounts of input, mistakes don’t appear consistently, but correctly used language does, and that’s what you acquire. This is also another reason why we don’t recommend intensive listening or reading. With intensive listening, you listen to the same sentences several times, analyze them, look up words you don’t know, etc. If there was a mistake in the input, or something in that input that is specific to the particular way that person talks, you can end up acquiring those mistakes or learn unnatural words and expressions. We also answer this question in our video FAQ (with English subtitles):