Nothing erotic has ever happened with me at numerous different legitimate health spas and massage practices over many, many years. I did visit a storefront massage place, staffed by Asian women, that might be considered the stereotypical "massage parlor" but they had signs that it was illegal to solicit or offer any sexual services, so I thought I was going to get a traditional massage and nothing more. Even the massage room had the same sign that was displayed at the front entrance - no solicitation.
The woman who was going to massage me asked me to disrobe and I did, lying naked on my stomach on the table. That was different as every legitimate place had at least sheets for coverage and the therapist left the room while I disrobed. But, she then proceeded to give me a very thorough, head to toe massage, and she was quite good at it, so I enjoyed it for what it was, a great massage.
When she had me flip over she continued the massage, never touch my penis or balls, but covering just about everything else. As I said, a great overall full body massage. When she finished she asked if there was anything else I needed and I used a free hand to grasp and wiggle my penis. She smiled and said "Okay!" got some more massage oil or lotion, and proceeded to give me a fantastic penis massage until I erupted in orgasm. She cleaned my up with a washcloth and towel, and I was on my way.
Was it a 'legitimate' spa? I'd say no, but with my being comfortable with being fully nude, and allowing her to massage me all over with no resistance on my part, she was comfortable enough to finish the job when indicated there was one part of me she hadn't massaged yet.