1. A search results optimizer system comprising: an electronic database configured to store information relating to available items and search requests for items; a conversion estimator configured to receive through a computer network a user search request for an item, wherein the user search request comprises at least a product category and a search criteria; a conversions module configured to access in the electronic database historical data related to search requests similar to the user search request, the conversions module further configured to analyze the user search request in conjunction with the historical data to determine one or more characteristics of the user search request, wherein the conversion estimator is further configured to search, using the one or more characteristics of the user search request, the electronic database for a plurality of available items relating to the search criteria, wherein each of the plurality of available items is pre-assigned a predicted conversion factor, the predicted conversion factor generated by inputting stated metadata and derived metadata into a conversion factor formula, wherein the stated metadata comprises attributes of an available item that are obtained from a product description provided by an advertiser or supplier of the available item, wherein the derived metadata comprises attributes of the available item that are identified based on characteristics of the available item and that are not stated in the product description provided by the advertiser or supplier of the available item, wherein the conversion factor formula is based on a linear or logistic regression analysis; a ranking module configured to generate a search results list based on results of the searching by the conversion estimator, wherein each item in the search results list is in the product category and each item in the search results list meets the search criteria or relates to the search criteria, the ranking module further configured to prioritize the search results list based at least partially on the predicted conversion factor, and to output the search results list through the computer network; and one or more computers configured to operate the conversion estimator, conversions module, and ranking module, wherein the one or more computers comprises a computer processor and an electronic storage medium.