9. The computer-implemented method of claim 1 , wherein the second component score representing a measure of quality for the item listing is calculated as a probability that an item listing will conclude a transaction if displayed in a search results page, the probability derived based on an analysis of observed metrics representing a measure of performance for item listings determined to be similar.
1. A computer-implemented method comprising: processing a query to identify item listings that satisfy the query, each item listing comprising data representing one or more attributes of a product or service offered for sale; assigning a ranking score to each item listing that satisfies the query, the ranking score derived as the product of two or more component scores including a first component score representing a measure of relevance between search terms in a search query and the item listing, the second component score being independent of the query and representing a measure of quality for the item listing, the measure of quality being based at least in part on at least one of (i) an attribute of the item listing determinable at a time of listing, or (ii) an observed sales performance of the item listing or an item listing similar thereto; and presenting the item listings that satisfy the query in a search results page, the item listings positioned in the search results page based on the ranking score assigned to each item listing.