The Better Business Bureau is as much of a joke as the companies that get reported to it. The BBB is in bed with many companies, and to become a "member" of the BBB, all you really need is some loose change.
Furthermore, once a company gets a few complaints that they're unable/unwilling to resolve (and hence, they then have a tarnished record), they have no real motivation to be concerned with future complaints.
Lastly, most people do not check with the BBB BEFORE using a company... they only investigate a company's history AFTER they've been screwed, thus completely negating the whole point in the first place.
The BBB really just serves as a mechanism for you, the screwed consumer, to prove to a court that you dilligently tried to solve the problem by all means available prior to suing.