The winners of the auction are generally determined by something called ad rank—a rank that considers the maximum bid set by each advertiser, which can range from pennies to unlimited (within certain restrictions), and an ad’s Quality Score. Other factors that influence an auction include the type of device being used, the searcher’s language preferences, their location, and the time of day.
SEO techniques can be classified into two broad categories: techniques that search engine companies recommend as part of good design ("white hat"), and those techniques of which search engines do not approve ("black hat"). The search engines attempt to minimize the effect of the latter, among them spamdexing. Industry commentators have classified these methods, and the practitioners who employ them, as either white hat SEO, or black hat SEO.[48] White hats tend to produce results that last a long time, whereas black hats anticipate that their sites may eventually be banned either temporarily or permanently once the search engines discover what they are doing.[49]