Online word-of-mouth has spread on almost every e-commerce website. While most of them use a global rating allowing consumers to judge any product, some introduced a multi criteria rating system on product features and linked services. Many researches in the field of multi criteria decision making has been focused on software and mathematical models, and not on the cognitive psychology aspect, especially in the field of e-commerce. We propose a state of art on three axes: (1) the role of trust in the purchase decision making process, (2) the electronic word-of-mouth with rating systems, and (3) problematic from a cognitive psychology point of view using the multi criteria rating. We present various research prospects on theoretical and practical level.