Well the law doesn't assume anything - brothels and brothel management/assisting are very clearly defined, whilst pimping is a completely separate offence which may or may not be taking place in any brothel or likewise between people who have never even met in person.
In my town there have been prosecutions of two women in a flat share, in other places parlours with a dozen prossies can open virtually twenty four hours a day without being troubled - it's even more of a postcode lottery than the NHS, but all it takes is a change in who's in charge to completely alter things. A co-operative sounds less pimpy and more treehuggy, but it's still every bit as much a brothel.
My only interest in the OPs claim (as I posted earlier) is that a punter seeing my ads would expect privacy and not to be directed to a premises like the one above, and I don't blame him. Other people won't mind in the slightest, but I think the idea that it's just like going to see any independent and can be advertised as such wants nixing
.