Ok, I used to help run a medium sized corporation, an internet retail site. We were registered with the BBB and I handled any complaints we got through them.
They are a joke. The BBB was set up to deal with brick-and-mortar storefronts and they did so reasonably well, but not great. Then came along the internet and businesses that operated on the internet. The BBB is not properly set up to deal with complaints of this nature.
There were a number of problems I dealt with concerning the BBB. Most of the time a customer would get a product, use it, then return it with no pre-authorization, we just got a box with a used product and a note saying "refund me". We would go back to the customer, tell them we can't refund them for used products and offer to ship it back to them for free. The next thing I would see is a complaint sent to me via the BBB by the same customer claiming they got authorization to make a return and we refuse to refund or send the product back. If we wanted to tell the BBB the real story then they would want proof that our side of the story was true. We had nothing to prove we didn't give a customer authorization and it simply wasn't worth the time to fax them a copy of the shipping receipt showing we sent it back to the customer. In the end we end up with an unresolved complaint.
That example accounted for about 95% of the complaints we received through the BBB.
The BBB is worthless. HORRIBLE companies will have their highest ratings, while solid companies that have great customer satisfaction will have low ratings. At this point in time they really are nothing more than an extortion racket... they tell companies they need to pay to register with them or they could end up with a low rating and customers won't trust them.
TL;DR version: The BBB is crap and so are their ratings.