Pay attention to what they say and claim to believe, and see if they walk the walk. Remember their opinions and see if they change depending on who they're talking to. And look for extremes in their behavior. It's not unusual for a sociopath to seem introverted and quiet, only to suddenly shift gears, and become the most loud and affable person you've ever met.
They also have other, smaller tells that you can use to spot them. Because their outward personality is a blank slate, they'll often talk in a somewhat monotone voice before they get to know you better (then they'll know how they should talk to you), and they'll usually leave a lengthy pause before answering any of your questions.
What they're doing is trying to gauge your personality, while they think of the "best" way to respond to you. You have to remember that since they can't really relate to most people, they treat human interaction like you might use a computer. Everything is a simple input/output to them. "If I say this in a certain way, I'm going to get a specific response."
Sociopaths also won't reveal very much about themselves. They'll always try to keep the conversation about you, because for them, every conversation is an opportunity to extract information. However, to make the conversation seem more genuine, they'll slip personal details to you from time to time. Pay close attention to these, because what they reveal to you is either an exaggerated truth, or an outright lie. Everything they tell you about themselves is designed to illicit sympathy and trust, and impart a sense of intimacy...read more>>>...