I just wanted to share my story, but sort of in the opposite direction:
Went to a spa that I've been going to for the past year now. It's a SF gay men's spa but it is very legit (according to reviews online and on this site). Each time I've gone, I've always gotten a professional and therapeutic massage, so I expected it to always be the case.
I went there again this past week, this time the masseur was someone new to me. I get into the room, remove my robe and lay under the blanket face down on the table.
This masseur then proceeds to remove the blanket exposing my ass and starts massaging my ass like crazy. As he is massaging my arms and legs, he puts my foot and hand right by or on top of his crotch. I felt so so so uncomfortable. I ended up ending the massage early because I didn't want to be near him anymore.
I'm not a prude by any means. I like the occasional sensual massage, but it has to be on my terms and I always ask for consent before doing anything. And I'm not saying that this masseur should have verbally asked me if it was okay for him to put my hand directly on his junk, but there are ways that you can test the waters by maybe grazing your crotch by the clients hand and seeing if they move their hand at all or watching for any subtle moans or movements to suggest that I was open to more. Instead during the massage, I made an effort to be as stiff as possible and intentionally angled my hand so that it would not touch his junk, or I would pull away at times. He didn't get any of the hints though.
All of this is to say: yes therapeutic turned sensual massages can be fun, but it is not okay if you (the client) or the masseur gives any indications that you are not okay with going further than therapeutic.