Someone has good arguments but you feel the person does not seem to be congruent - something is not right!

For a successful credible appearance congruency is essential.

Congruence is when all verbal and non-verbal behavior supports one single outcome or message.
Congruence is a state when a person’s words and body language match exactly.
If you want to clearly know the person’s state of mind, then observe the gesture clusters and their congruence.

Nonverbal signals have way more influence as verbal statements.
When the two are incongruent, most people rely on the nonverbal message and disregard the verbal content.

Be careful! Your body language is going to betray you.
An uncontrollable incongruence between how you are acting and what you are saying is going to say something you don't want.
Many people accidentally leak signals of incongruity simply because they are unconfident in a particular situation, such as making presentations in front of an audience.

Most people are quite intuitive about detecting mixed messages, and especially in business this can be highly counter-productive.
Knowledge about body language helps us recognizing if people’s bodies and voices are presenting emotions which are contradictory to what they are saying.

In almost all all business situations, people are more likely to succeed when they are congruent.
Management, customer service and sales are more convincing if they are accompanied by congruent body language and a congruent voice tone.