Paperback Writer wonders, in Perception: "how can you tell when someone on the internet is lying to you?"
Really good liars are hard to detect even when you're sitting face to face with them, actually. I know this from having had a number of friends in low places.
As for those who may be lying on the internet, I have grown suspicious of people who preface their criticism of the Bush administration by saying that they are lifelong Republicans or conservatives. This is supposed to give added weight to their views, I gather.