1. A computer-implemented search engine method of ranking a search results list, the method comprising: receiving, in a server device, a user search request for an item, wherein the request comprises at least a product category and a search criteria selected by the user; receiving, in the server device, a content publisher preference from a content publisher, wherein the content publisher publishes product data provided by advertisers or suppliers, and wherein the content publisher preference comprises at least a preference to maximize revenue or a preference to maximize user experience; searching an inventory database for a plurality of items matching the search criteria, wherein a predicted conversion factor has been pre-assigned to each of the plurality of items, wherein the predicted conversion factor is determined based on a linear or logistic regression formula, wherein the predicted conversion factor is determined by inputting metadata into the linear or logistic regression formula, wherein metadata comprises extracted metadata and implied metadata, wherein extracted metadata comprises attributes of a product that are obtained from a product description provided by advertisers or suppliers of each of the plurality of items stored in the inventory database, wherein implied metadata comprises attributes of a product that are provided by a third party source and that are not stated in a product description provided by advertisers or suppliers of each of the plurality of items stored in the inventory database, wherein a product category is associated with the linear or logistic regression formula, wherein the linear or logistic regression formula is generated based on an analysis of historical conversion rates for at least one product in the product category, and wherein the analysis of historical conversion rates comprises a probability that the user clicks on a particular product advertisement based on an analysis of historical user behavior; generating, in the server device, a list of the plurality of items based on the searching, wherein each item in the list of the plurality of items is in the product category and meets the search criteria selected by the user; applying, in the server device, to the predicted conversion factor for each of the plurality of items a value to be paid by a supplier of the item, wherein the applying is performed if the content publisher preference is to maximize revenue; prioritizing, in the server device, the list of the plurality of items based on the predicted conversion factor; and outputting from the server device the list of the plurality of items in the order based on the prioritizing, wherein the server device comprises at least a computer processor and an electronic memory device, wherein the preference to maximize user experience comprises a preference to list items in the plurality of items with the highest conversion factor near the to of the list of the plurality of items.