I think you're over generalizing but yeah some people will believe lies from people they like fairly easily or other manipulators. Generally though people don't lie unless they have a reason or motive for it, unless their a compulsive or pathological liar. Without a good understanding of situation you may not understand someone's motives for lying.
I'm not sure if you've seen the movie Scarface where near the end he has his breakdown where's he's like you need people like me to point the finger and say that's the bad guy.. What does that make you good? You're not good you just know how to lie and how to hide. Then he continues and says I always tell the truth even when I lie.
By the last sentence I quoted he means even when he lies there are signs he is lying, so it's still possible to decipher the truth.