I can't credit bucket shops with much of anything, but I will say that while the "one man, one coat" idea is pretty firmly held in Scotland, things are a bit looser in England, where it's not uncommon for a man's arms to be borne by all his heirs. So, in that sense, England, at least, has the concept of "family" arms.

Of course, if you haven't done research, then you may not (or rather, very likely don't) have any relation whatsoever to the armiger who simply happened to share your last name. If you did, you probably wouldn't need the guy in the mall to tell you.

Do the people selling "family histories" and "family arms" explain any of this? No. So, I think they're doing people a disservice and creating a false impression of what heraldry is and means. For not much more money, you could get the American College of Heraldry to create your very own arms, which would be more meaningful, and would have a definite connection to your family. Sure, they'd be "assumed" arms, but there's nothing particularly wrong with that (in fact, you could argue that it's the really, really old fashioned way), and I think a better investment.