Many times.

We had a top-performing sales associates who was very charming, but rubbed me the wrong way. When we first interviewed him, I had a feeling that he wasn't trustworthy, and I shared my concerns with the owner of the company who hired him anyway. Turned out that he became our top performer by selling huge amounts of product to his friends, who would file complaints about the product and process returns after the commissions had been paid. He would split the commissions with his buddies. You should have seen him strut around and brag about his sales performance, it was unreal. Well, literally unreal!

Another instance, I had a very bad feeling about a male friend's new female friend. She was bubbly, very outgoing, always laughing and smiling, and everyone seemed to like her except me. She could tell I didn't like her, and actively tried to drive a wedge between my friend and me. Didn't work, since we had been friends for decades, but she tried hard. She was always touching guys inappropriately, being way too flirtatious. I also had a feeling that she was fake and petty, and had no backbone, but I couldn't say why. I kept my mouth shut because everyone else loved her. Ultimately, she ended up fooling around with a guy in our group, which destroyed his relationship and our group of friends drifted away from her.

I could go on and on. It's funny how being able to identify d-bags ahead of time usually costs me. If I share my gut feeling people think I am being too harsh, so I generally keep it to myself. Once the cat's out of the bag, there is no benefit to pointing out that I noticed early.