My husband & I had to learn this the hard way. He had a nice looking, well spoken, charming and seemingly honest jr partner who stabbed him in the back and stole a portion of his business. During the time they were working together, I’d notice things he said and did that I distrusted and I told my husband and he always dismissed it. We came out of it fine but only because my husband realized I was right and gathered all the damning evidence. So it may not show in big ways but when people do sneaky things or “out of character” pay attention!!!