One man’s puff is another’s positive spin. One woman’s bluff is another’s best foot forward.
Lying about a material fact in a negotiation is unethical, and it is almost certainly grounds for legal action. In certain circumstances, creating a false impression or failing to disclose material information may be a formal ethical breach and actionable as well.
Even a cooperative, creative negotiator, however, must have a sense of strategy. As long as what you bring to the table has real value, you need not reveal all the circumstances making you desperate for a deal. Thus, if you are negotiating the terms of a job offer, there is nothing wrong with describing the major projects for which you have been responsible, and the likely next step on the corporate ladder in your current company. There is no shame in describing your achievements in a positive light. You need not mention that the new division president is impossible to deal with or that one or two projects have not turned out well. This is not hard bargaining; it is effective self-advocacy or salesmanship.