How do you know which shops to ask for this stuff, at? There's a beauty salon type place in one of the West Brom precints and I have wondered, but don't want to be punched in the face! 
You don't unless someone has been before and has reviewed it.
Even then there are no guarantees. Some masseuses do and some masseuses don't hence the WSWS.
Even if you see the same masseuse who has been reported on positively before, there are no guarantees hence YMMV.
Chinese ladies usually do and will usually whisper in your ear after about 20 minutes.
Most Thai ladies do but are more reticent and will often finish the massage and say something like, "anything else today".
English ladies, working in a shop, probably don't.
Other clues are, if they open 7 days a week and stay open beyond 6pm, then they probably do.
