Even when your mark doesn’t believe you, you often weave a credible second story explaining why you had to lie once already.
Benefit: When you fail a Bluff check to fool someone, you can attempt a Double Bluff. This requires you to develop some story by which you admit your first Bluff was a lie, but explain it away as part of a new lie. (“No, you’re right, I’m not a spy for the king. In fact, I’m an assassin, sent to kill the king and end his tyrannical rule. But I had no idea you were one of the few locals who had seen through the king’s front of fair treatment and goodness, so I had to lie to you to conceal my true purpose.”) This second attempt is at only a –2 penalty, instead of the normal –10 penalty for a second effort to deceive a subject with Bluff. If your second attempt fails, however, no third attempt is possible, regardless of what stratagem you employ.
Adventurer’s Handbook: Genius Guide Volume 1