1. A computer-implemented method comprising: determining, by a query reissuer that includes one or more processors, a first estimate of quality of a first set of search results that a search engine identifies as responsive to a user search query received from a user device; classifying, by the query reissuer, the first set of search results that the search engine identifies as responsive to the user search query as unacceptable based at least on the first estimate of quality of the first set of search results; and in response to classifying the first set of search results that the search engine identifies as responsive to the user search query as unacceptable based at least on the first estimate of quality of the first set of search results, transmitting, by the query reissuer, an instruction to a query reviser to generate a modified search query for submission to the search engine.