It's actually not that difficult to tell when a person is not being truthful (sincere). The obvious sign is when he (she) blinks his (her) eyes involuntarily when he (she) talks to you (unless he's (she's) already an expert in deception and he (she) can lie through his (her) teeth). When he (she) talks to you without facing you but instead facing another direction, that's another sign that he's (she's) not being truthful (sincere), unless you know that he's (she's) shy. And another sign that he's (she's) not being truthful (sincere) is when he (she) turns his (her) head to the right when he's (she's) talking to you.
Dare to Dream