They actually made it illegal in Germany (with the new laws) and any sex worker advertising BB in Germany can get arrested now.

This OT's question does pop up from time to time.  As for "on the sly", meaning "informally", not advertised as such -  I'm pretty sure there are other variants, too.  I agree that the term, demonisation is probably very accurate, used by escorts against other escorts.   People do as they please with their body, be it a whole-male fist fisting or otherwise.  I doubt this industry is as regulated as people would have liked. It's not.  I don't know enough about this new German legislation.  Maybe, there are unwanted abortions amongst vulnerable service providers, increased infection rate/ concern for incurable STIs, protecting vulnerable women, who knows?   I also agree that I have not seen a single post by escorts, who would do it only with their longstanding regulars whom she "gets on" with to keep these regulars.  I wouldn't particularly call it this is "on the sly".  She is probably forced into it over time covertly as she's afraid of losing the incomes if she wouldn't consent.

I have very few regs - thankfully, they don't ask any risky stuff, if he did, it would have really signalled the end.  But I have had quite a few repeat men, who expected it at some point, or even a year later, and moved on, rejected.  There are condom rippers.   I had one with one of the long-term regs whom I was itching to get rid of.