If you see it openly advertised, I assume they are trying to increase revenue.

If you're looking at Kgirls, then I belive it. If not, then maybe we define a lot differently lol. I only see a small number of non Kgirls actually advertise it, and it's usually with an upcharge and recent test expectation. Kgirls idk what their deal is that they do it so cheap, don't require tests, and likely are hitting 5+ guys per day. I highly do not recommend seeing a Kgirl. I have done it a few times, and they are never the girls in the picture and you're basically doing BBFS with girls who are getting cum dumped by numerous guys a day.

If you want BBFS get into an arrangement.  This way, in theory, it's only the two of you.  Even with clean tests, you don't know how many clients she's seen.

a guy can fee comfortable seeing a lady that advertises BBFS.  That's just gross.  That said, I can assure you that a lot of ladies do very, very, selectively provide it to select regulars that they feel confident are clean.  So you should always assume a lady you are seeing dishes out at least a limited amount of BBFS.  They might not, but you have no way of being sure.  

Also, I'm sure a lot of scam ladies advertise BBFS, but they obviously won't deliver because it's a scam.  Seeing that in an ad is actually what I consider a scam red flag.