I've faced "being taken advantage of" twice during a massage, once by a top and once by a bottom. Both were many years ago, when today's medicines for HIV and Prep were not available, you were positive for weeks or months before it could show up on a test, and HIV usually still meant AIDS eventually.
The first was a tall, muscular masseur. We were part way into the massage on a table and I noticed he was paying a lot of attention to my butt. I'm sure I was appreciating it. The massage stopped for a few moments and I heard some noise that in retrospect I should have recognized. He was putting on a condom. Then, all of a sudden, he was knocking on the door. Fortunately, I was tight enough that he got nowhere, and I made plain in no uncertain terms that what he wanted was not going to happen. We finished the massage, which except for this incident was pretty good, and I think there was also an HE. I did not tip and never went back. The good news was that penetration did not succeed and that he had on a condom.
The second was a much smaller guy with a very attractive athletic build. I think it was my second massage with him, but it was long ago enough that I don't remember for sure. He gave a very good massage on a table. After I flipped over, he was sitting on top of me. I was aroused, naturally. He was massaging my chest, I think, and then all of sudden in a very deft and astonishingly swift move he slid himself onto me. I came almost instantly, before I could pull out or pull him off of me. I did not have a condom on, and made clear that I was upset about the risk. He told me he was negative, but I knew that was not good enough. I had anxiety about it for months until it was long enough after the experience that I could be sure of having gotten nothing from him. I was also startled that he took the risk he did. He actually seemed something between startled and bemused by my reaction. I did not tip and did not go back.
In retrospect, I should have walked out on the first guy at the moment he tried something. He was big and strong enough that, if he wanted, he might well have been able to hold me down and force himself in. I don't know what, if anything, different I should have done with the second guy.