If your charming boyfriend or husband sometimes seems too good to be true - chances are he is, according to research by Bolton University.
Chris Kirkman, senior lecturer in health and social studies at Bolton, has been studying the experiences of women who have been duped by charming arch liars, with other lives and often other wives in the closet.
She said she planned to bring her experience to the wider world, teaching women her tips for detecting a psychopath in the bedroom.
Dr Kirkman said: "There is no doubt that this is a big problem - I had lots of calls when I first advertised for victims. The eerie thing is the women had almost identical stories. These men weren't just doing the same thing they were saying the same thing."
Her local focus group included a woman who was married to a man for 20 years before discovering that everything she thought she knew about him - from his name to his job - was a lie. The biggest surprise was that he had another home and long-term wife.
Dr Kirkman said: "One woman located six women who were all seeing her husband at the same time, each of them believing that she was the only one."
Dr Kirkman's main piece of advice was that women should avoid intelligent charmers, especially when they come bearing flowers.
She warned women to be alert if their new partner wanted to spend lots of time with their friends or family but was anxious to keep his own out of bounds.
"They are pathological liars, but it is also about thrill-seeking," she said. "Being in the secret service is a popular fiction. But one of the most frightening things was that one of my women had been duped by someone who was actually in the CID. He had many other women. It was quite amazing."