There are several web-based classified that list these businesses. There are lots of suggestive phrases used and photos of attractive girls who couldn’t give a real massage if their life depended on it, but they rarely put it black and white for obvious legal reasons.
Even an otherwise legit massage place may have a masseuse or two who will give a happy ending. https://theporndude.com/erotic-massage-sites Generally the girl will be rubbing your hamstrings or inner thigh and their hand will “stray” a little towards your crotch; they’ll usually ask “is that OK?” A response in the affirmative and they’ll ask you more leading questions. Sometimes they’ll breathe in your ear or lick it…
In my experience, they’ve never negotiated a price beforehand, though it’d be helpful! Bring 5s and 10s so you can make exact change but I’d expect to “tip” about $45 for a handjob on top of the agreed-upon cost of the massage. I’m sure this varies from one place to the next.
You’re likely to get better service and a far more attractive girl by looking for a FBSM (full body sensual massage) from an independent provider. Other services may be on the menu. Generally the terms sensual, full-body, erotic are all code from something not quite legit.