The view that the practice is rampant because it is mentioned in one provider's ad(s) and has been mentioned is some reviews (which I can't verify since I don't have BCD access and am not interested in since I don't hobby) seems rather alarmist. Especially the idea that it may be due to economic competition making more and more and more and more and more girls into BBFS practitioners.
Oh, I think the economic incentive is there, but not in offering BBFS, rather in spreading rumors that so-and-so offers BBFS. In the 15 years since I've either hobbied or participated on hobby boards there are a select few accusations/allegations that do wonders for tainting a reputation and scaring off a provider's clientele that are hard to overcome: BBFS, STDs, drug abuse/addiction, having a pimp, going psycho/stalker/outing somebody. In more competitive times, it seems that more and more of those sorts of rumors fly around.
Sometimes the motive to hurt somebody's business is because of a personal grudge or vendetta (whether it's a hobbyist, provider or agency spreading the rumor). Sometimes it's for someone's financial benefit as the beneficiary gains clientele that the slandered person(s) lose(s) (whether it's by a provider, agency, or a hobbyist seeking to curry favor with a provider or agency).
Assuming it's a one-on-one session and not a threesome or foursome or more, the only people that absolutely know for a fact what occurred, BBFS or CFS, are the parties in question. Either the giving or receiving party has to out both of them. Anything else is a rumor. It's not even a he said/she said, it's a somebody said.
Why would a hobbyist lie about getting BBFS in a review? Well, maybe he wanted it, but didn't get it so he's gonna say he got it to mess with the provider's world. Guys that disapprove won't see her and guys that want it will book with her expecting it, get disappointed, perhaps leading to bad reviews. Plus, after the public flogging, those that are part of the BBFS subculture may befriend him and point him to where he can get BBFS. All he has to do to see other providers is never identify himself by the handle that posted the BBFS review.
Why would a hobbyist spread rumors about knowing that so-and-so barebacks? Well, he could have a grudge or think he's doing his favorite provider a favor by hurting her competition. Or it might not even be about the act of BBFS or even a grudge about the provider. Some people will lie for the attention whether it's good or bad, whether other people get hurt or not. Some want others to think that they're "in the loop" and privy to all sorts of confidential information. If it blows up in their face, so what? They can reinvent themselves with another handle. This sort of juvenile attention-seeking may sound nuts, but there are plenty of people in the civilian world that will use their real names and claim to know what really happened at Roswell, to have seen the Loch Ness Monster or Bigfoot to stroke their ego and need for attention. Do you really think there are none of them in the hobby, especially when they can hide behind an anonymous internet handle?
Hell, some hobbyists and providers may spread rumors just because they like to see all the commotion and all the fussing it causes. Like Alfred tells Bruce Wayne in The Dark Knight: "Some men just want to see the world burn."
Everybody knows BBFS happens. Perhaps for a variety of reasons. But hidden agendas also happen and for a variety of reasons as well. My skeptical nature leads me to believe that hidden agenda-driven rumor mills are much more common than BBFS.