What are search quality raters?
Search engines hire professionals word-wide to rate the quality of their search results. For example, Google contracts over 10,000 professionals to review and rate the quality of their search results worldwide. Search engines provide them the real search queries conducted by the real searchers. These professionals conduct the same search queries and rate the quality of top search results. That's why these professionals are called search quality raters.
These search quality raters can't alter the low quality search results. It is also not necessary that the search engines will remove those search or reduce their rankings. This data gathered by search quality raters is used to create an algorithm to escape those low quality results in future.
However, in future, when the algorithm is implemented, all the low quality search results won't appear in top search results including the ones, which are reviewed and not reviewed.
These search quality raters use the set of guidelines to rate the search results, which is provided by the search engines. For example, Google has following guidelines to assess their search results. The main motto of search quality is to assess, whether the top search results meet the need of users or not.