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Business X may easily gain more than business Y loses, if the site cleanup yields a site that's easier to find, has more descriptive content, and is more accessible. Y's previously higher ranking may have caused some potential buyers in a product space to abandon looking--even if temporarily--due to lack of time or loss of interest. X might have a good product that missed some sales due to a "meh" reaction to Y's previously higher-ranked site.

Marketing effect can be difficult to quantify, but it's about more than ad dollars and the bottom line is definitely not a zero-sum game. While SEO doesn't lack for bad actors, white-hat SEO can help grow markets.