For performance reasons it is common practice to set option values for custom fields to be integers while having the display values as strings. However this configuration makes using the Search Builder with custom fields a real pain since you need to go to the Custom Field admin section to lookup the integer that you need before you do your search.
Furthermore this isn't obvious unless you know how the custom field is setup, you read the Search Builder documentation in fine detail, and you have permissions to visit the Custom Fields admin section.
In order to eliminate these extra steps the input could be validated before the query is built. First check if the user input is a valid option value for this field, if not then check if it is a valid display value, if so then use the matching option value.