I think 7 is probably right. Most gun owners do not know the law. They think they do; they don't.
I've been to gun shows and argued with dealers about the legality of something they had on their table (ironically twice was exactly as Driftpunch had stated - attaching a forward grip). One guy told me, "I'm a dealer, I know the law!" Well, sh*t pal. Anyone with a clean record, proper zoning and $200 can get a FFL. I've got an FFL and a JD, but even with that, I'm smart enough to know I don't know everything in the law, and I'm always open to research and learning something new. For better or worse, I don't say anything at gun shows anymore. For the most part, they don't want to know the law, especially if it conflicts with their interests, and I get tired of banging my head against the wall trying to be helpful. If he doesn't know the law, he'll figure it out when/if he gets busted.
Not to open up this can of worms again, but for an example, look at the debates on this board and in the leagl forum about "pre-ban" receivers. Most people don't know what constitutes a true "pre-ban" receiver, or what the gov'ts burden of proof is to convict you on possession of an illegally assembled "asault weapon". Its one hell of a lot lower than most people could ever imagine.