It In the UK we don't really have massage chains and so even legit, qualified massage therapists usually work out of their home where there's always a better chance something might happen.
That said about 10-15 years ago I went to one guy who had a very professional set up in his home. It all looked like a medical office with his qualifications and other paraphernalia displayed, he wore quite a formal looking white outfit and got me to fill in and sign a form about my medical history.
However he was also unphased when I said no to draping and it felt like he lingered on working on bits of me that got a audible reaction particularly around my glutes. Then there was a slight pause and then he moved up to work near my head and through the hole I could see he was no longer wearing trousers. Sure enough he was completely naked and soon when he was back at my side he rested his hardening cock in my hand.
He then climbed on the table and rubbed his naked body against mine. Eventually I turned over and we kissed and 69d for a bit before we both came over my chest and face. After he cleaned me up he finished the massage still naked.
I tried to see him again not long after but schedules didn't match and where he lived was awkward for me to get to. Not long after he started working out of a studio space in a health and Wellness shop which was much closer to me. I went along as the massage had been good but expecting nothing more given the location but as I stripped off for the massage he joined me in getting naked. So for over 10 years, on and off, I'd go along for a mutually naked massage that would always involve some kind of fun, at least kissing and wanking but sometimes even fucking with the added thrill of no one outside the room knowing what was happening.
Sometimes when he was particularly horny the sex would overwhelm the massage to some extent, so a few times he had his tongue in my hole 10 minutes in getting me ready for his cock. It fizzled out for various reasons around Covid. I still see him sometimes but it's now pretty much above board though he's still fine for me to be naked and still lingers a bit on the more sensual parts and seems happy if that makes me hard.