I have a son we adopted out of foster care who is a chronic liar. I often use words like "allegedly" and "claims" when I talk about things he tells me. Sadly for him, if he were to tell me that he'd been robbed, beat up, or victimized, I'd use words that cast possible doubt on his story. I've been burned by false reports from him many times. My wife and I are trying to help him understand how important trust is so that people will believe him. The whole Peter cried wolf thing.
There are others in my life that I trust without question. I'd use different language to describe their claims.