Picture the following scenario. You are interviewing someone for a job and they spout off all sorts of wonderful things about themselves. You call their last boss and get a less than desirable recommendation. Whose words do you believe?
Or how about this. You are at a cocktail party and a stranger comes up to you and starts telling you how cool their marketing software company is. A little while later you are having a conversation with another stranger and they tell you that they recently purchased and are loving a different marketing software company. Whose recommendation are you more likely going to check out?