YouTube Videos A Scam? Or Not?

Tim, Hayley and McKayla's blog post mentions that people might think the video one watches advertising a product on YouTube could be seen as a scam. Good point. How do you determine whether or not a video that you see is a scam or not? Isn't that sort of the same when we see information online every day? How do we know that what we see is legit? Remember when we watched the Blendtec videos? Do you think some people thought that was a scam? Thoughts?