How do you find out if someone is telling you the truth?

I hate it when people lie to me. Actually I despise it, and I always make it clear when I make new friends. All my family members know that too. So I in return don't lie to them. So I just assume that whoever I am conversing with is taking me seriously and is honestly telling me the truth. When I ever find out that a person has lied to me, it is over. I am not a very forgiving person. Partly because gaining my trust is hard. Other than that, if it is someone I don't really know I just follow my instincts; sounds cheesy but true. I can almost sense it from the language. I can feel if the person is lying through the words he chooses to say. Body language can also be quite helpful especially if the person is fidgetty or sweating, or can't even look you in the eyes. So if I meet someone I flatly think they are lying unless they say something to convince or prove me otherwise. As I said I don't trust anyone, and if it is someone I don't know then not at all. Better safe than sorry is my theory. Think of all people as liars and whoever proves themselves otherwise then they aren't. But of course that is just me :)!