Depends on the circumstances I suppose. First thing I would ask myself, how important is it?
I can remember once years back, had a friend that I would refer to as a 'bullsh***er'.
This person was/is? a chronic liar, but it was mainly about telling tales that involved himself, don't recall if any of the lies would have been characterized as serious. But it got to the point, don't remember if I confronted him or just gave him a skeptical look after he told me a tale that was slightly implausible, he pleaded that 'it was true' so he must have recognized himself that he was a bullsh***er.
I have a 'friend' now that would be classified as a 'chronic liar'-google it-I take just about everything she says with a grain of salt, no sense in 'confronting' her, that never went well and it's not my problem.
The odd thing is, in her own way she can be very honest about herself but in the most indirect fashion imaginable.
The whole subject brings me back to my particular problem, trusting people that don't merit my trust and not trusting people that do. Good post!