Positive-negative asymmetry, involving positivity biases and negativity effects, may be relevant. Putting forward evaluatively negative information may improve the negotiation in that negative message contents tend to be more informative that positive ones. However, they may spoil the negotiation because they elicit emotional aversion. Hence it may be worthwhile to know that mildly negative messages may be recommended. A similar restriction does not apply to evaluatively positive messages. See the section on “backbiting” in the chapter below:
Chapter Positive-Negative Asymmetry in Evaluations: The Distinction ...