I've never been offered BBFS, but then nor am I a frequent pooner, so I haven't had many opportunities to be offered the service. Noe have I every seen anyone more than once.
My reading of this, particularly in terms of the higher end ladies, is they want to pick and choose who they are comfortable going that far with. And so my advertising that it is out of the question decreases the chance of that question coming up.
There is, apparently, a market for this. But why someone at the higher end would risk their health in this way does puzzle me... though maybe if they don't have a regular partner outside of the industry, the feeling of skin-on-skin maybe something they too are needing on a regular basis, and so they take the risk.
I don't know. I'm speculating here, and it is highly unlikely we will have a lady who endulges in this practice enlightening any further.
Maybe an acquaintance of one might be able to add to this?