You tend to get much better results with using a third party company (such as the BBB) since the company's action towards the company stands to have much more weight than a single consumer's. It's similar to governmental regulation, except it tends to scale more appropriately with size. E.g. 'Ma and Pop BnB' are generally not going to end up facing BBB complaints since they can resolve things 'locally.' Whereas with governmental regulatory systems 'Ma and Pop BnB' is treated in many ways the same as multibillion dollar multinational "BnB" and inadvertent noncompliance can be devastating, even when such inadvertent noncompliance in no way negatively affected anybody as you invariably end up with some rules that make sense for multinationals, but not necessarily e.g. a couple of retirees renting out a spare room.
[1] - https://www.bbb.org/us/ca/san-francisco/profile/rental-listi...
https://money.cnn.com/2015/09/30/news/better-business-bureau...
Beyond that, the advent of modern communication has taken a huge bite out of whatever relevancy they might've had. Why complain to the BBB when you can complain via Yelp/Google Reviews/Facebook, etc. and have a bigger impact.