A user review refers to a review written by a user or consumer of a product or service based on the author's own experience as a user of the reviewed product. Popular sources for consumer reviews are e-commerce sites like Amazon.com and Zappos and social media sites like Tripadvisor and Yelp. E-commerce sites often have consumer reviews for products and sellers separately. Usually, consumer reviews are in the form of several lines of text accompanied by a numerical rating. This text is meant to aid in shopping decision of a prospective buyer. A consumer review of a product usually comments on how well the product measures up to expectations based on the specifications provided by the manufacturer or seller. It talks about performance, reliability, quality defects, if any, and value for money. Consumer reviews, also called 'word of mouth' and 'user-generated content' differ from 'marketer-generated content' in their evaluation from consumer or user point of view. They often include comparative evaluations against competing products. Observations are factual as well as subjective in nature. Consumer reviews of sellers usually comment on service experienced, and dependability or trustworthiness of the seller. Usually, they comment on factors such as timeliness of delivery, packaging, and correctness of delivered items, shipping charges, return services against promises made, and so on.