The majority of beauty salon/massage shops are "knocking shops" but does depend on the lady...I've "knocked" in many shops all over Patong
But for some of the "classier spas" like Bali Hai you won't get more than a BJ...the ladies there are threatened with losing their job if it's known they've done any "knocking".
"Classy spa" Tailife fairly new behind the Taipan is very pleasant for a couple of hours on a hot afternoon but don't expect any happy endings there
http://www.tailife.com