If one query matches multiple results, you can observe which result users tap and sort that one to the top. Or, if the user types in a query, gets no results, then types in a similar query and selects a result, you know that the first is likely to have been a misspelling/alternate spelling. If lots of users type in a query and don't get results, then that query can be flagged for further investigation. And so on.

All of this in addition to users reporting erroneous results.