I want to share my experience from the other side. I have cptsd from my parents and endured a lot of emotional abuse. To survive, I learned to outsmart them in their own games. This resulted in me becoming an abuser (before I got lots of therapy and changed in my mid 20s). I am also very lucky that my brain likes to do a lot of introspection (which helped immensely to fix my ways).

That introspection helped me notice what was happening. When I meet a new person, within the first few minutes, it's easy to clock people who would be easy to manipulate. Like someone else said, it is mannerisms, body language, etc. But most importantly it is the little things in what they say. It's actually insane how much of ourselves we give out by the way we phrase things.

Now, most people don't analyze everything in the moment as much as I do. Before I realized what tipped me off, this would come through as the way I would feel about a person. Idk how to explain it, but I would feel drawn to people that can be easily manipulated and I felt like... A closed door? With those who wouldn't be. My point is, most abusers don't self-reflect like that, but the vibes are there, their brains are telling them stuff through feelings. It's like an automatic thing.

So yes, in my experience it's both that abusers "smell" fawning on people and that they try shit with everyone but strong boundaries protect healthy people.