How do you know if a perfect stranger is telling the truth, is not quite sane or is a very good compulsive liar?

I met a lady while I was riding the Greyhound the other day, who proudly told me that she was a Christian author. In fact, she claimed to have written the famous poem Footprints in the Sand. Her story was very in depth and mostly believable but I began to suspect her truthfulness. When it came right down to it, there was just something about her (besides some of her weirder ideas) that didn't feel right.

She said she wrote Footprints when she was six and, as the daughter of writers, was able to publish her poem fairly easily. She has written other Christian books but doesn't care to collect any royalties because she wants her books to bless others. Nice story... could be true, but is it? If she was so intent on remaining anonymous then why was she so quick to tell me that she was an author and then be so proud of herself?

But what really scared me were her "Christian" beliefs. There is no hell, she said, Jesus will witness to everyone when they die. Not only that but all beliefs are justified and it's a matter of cultural as to what which religion is right for you. If you are Asian, then you should be Buddhist, not Christian. If you are Middle Eastern you should be Muslim not Hindu. She still believed that missionaries are good but her logic for justifying everything was crazy. Either she goes to a whacky church or she's really mixed up a few biblical truths.

I think I'd be afraid to read any of her books.

This whole experience made me think: How do we judge if a total stranger is truthful, mental or a compulsive liar? Some people are really good at feeling people out to see if they're lying. I'm pretty bad at it.