Negotiators tend to think they are more transparent than they truly are. They believe that their negotiating partners can discern their thoughts, and negotiating positions, when in fact the partners are clueless. See the experimental evidence from this recent paper by Leaf van Boven, Thomas Gilovich, and Victoria Medvec. There is good evidence that we send involuntary signals of our own trustworthiness. Still, we do not always have a good sense of how those signals are interpreted by others.
The basic result may stem from a kind of excess sympathy. The negotiator tries to put herself in the position of the “other mind,” but cannot eradicate the knowledge of her own bargaining position. So the model of the other mind contains more self-knowledge than is rationally justifiable. Related results have been found in other areas. Individuals overestimate how much others pick up on the cues from their facial expressions. Similarly, individuals who are laughing think they appear more expressive than they do to others. As for bloggers, well, they probably think that readers pick up more of the nuances of their writing than is the case.