You missed a key part of the story where the undercover agent told the bitcoin seller that he was going to use the bitcoins to purchase stolen credit card information. That's the key part in this case, and probably the only reason an arrest was/could be made.
This is an interesting point and one that I missed the first time I read the story.
Well, ok, but so what? If I go to a hardware store and tell the clerk that I'm buying this drill bit so that I can drill holes in my neighbor's tires, is the clerk somehow criminally responsible for selling me the drill bit? The clerk sold me a tool, and how I use it is my responsibility, not his.
I'm going to love watching how the State of Florida tries to base a prosecution on this nonsense.
But yes, I know...we're talking about Florida...Nick Navarro still working there? ;o)