In my case, it was what I discovered after having it explained to me during a job interview why the salary I was asking for wasn’t feasible. The company straight up said they couldn’t afford on top of the recruiter’s commission. I had assumed the recruiter was representing the company, but after that experience I spent time learning about the murky side of recruitment.
I had a really awesome boss who probably overshared about stuff like this but a lot of it also comes with general distrust in the business world. People are out to make a buck and they'll do it anyway they can. Every time you come across a business, consider how it works and where their profit comes from.
A tactic I've used in the past is buying a burner number (prepaid sim), called recruiters with a fake name, number and resume and asked them to provide details about the job which many of them name completely. The ones that don't generally indicate that other recruiters do exactly what I'm doing to them in order to steal clients.
I don't feel bad about screwing over an industry which has no place in the modern world, particularly when they're opportunistically trying to make a buck from me and/or my future company while adding very, very little value :)