I would suggest you listen carefully. When someone discusses their past, a subject on which they would be well versed, they may change the details of chronology or circumstance in retelling. They may provide one version to you and a different one when speaking to someone else. Habitual liars frequently lose track of what they've said and to whom they've said it, so you may hear the "revised" version in subsequent discussion. Much like a false or exaggerated curriculum vitae, certain details will change in retelling. Over time, you will witness one event or another and, when describing it, the liar will color details differently.
I place no reliance on habitual liars; their words are worthless, especially on issues that matter, and there is a manipulative element to their conversation. They're selling themselves, but it's false advertising. They made add just enough humility to appear credible, but there's an underlayer of duplicity.
I can overlook the "sea stories" or the evolving description of the fish they've hooked, but on issues of greater importance or in written reports or testimony, their words are valueless. I do not trust liars nor do I put them in positions of trust. Credibility is a foundation of trust and friendship. Like many of us, I have seen my share of disappointments.