Disbelief Is Not An Accusation

Not believing, being skeptical, having suspicions is an absolute human right. It does not require to present any evidence. Even if your disbelief implies that your interlocutor may lie(it's only a probability). This is your interlocutor's burden to accept your disbelief or suspicions. You must present evidence only if you make a radical accusation.

Force someone to believe (which is impossible) or silence him, just because not believing implies that your interlocutor may lie, is an insult to intelligence and affects freedom of speech.

"I can't believe you" is not equal to " you are a liar"