It's not simply hype - there's some evidence behind this. Just seeing the kid play should answer some questions. There's a lot of video out there on all the guys now - and while most of us aren't NFL scouns, there are certain judgements one can make based on such, even on "great play" highlight videos.
For example, for me personally, I think Mendy had a lot of hype. Yet nothing I saw on video made me feel he warranted it. Product of the system, not that great a back (my .02, not looking to debate it here). Thus, I stayed away. Hype not bought into.
McFadden - tons of "anti" hype. But I liked him in every college game of his I watched. Liked what I saw on video, too. Liked what I saw in preseason. Drafted him with confidence. Hype (anti in this case) again not bought into.
CJ3 - Saw one game of his in college. Liked him a lot. Still, was smaller... watched more video... wow, he's scary fast... He was drafted to the perfect place. He also fits into my personal theory of just how the NFL/FF is changing (CoP backs that are more than simply CoP). Hype bought into - I think he's legit. Drafted at 4.1 of a new startup, traded for in another.
"Untradeable" studs come from somewhere. You either get them early (meaning you may be labled as buying into the hype when it's there) or you may end up on the outside looking in (obviously, this is more from a dynasty perspective.)