Highlights of the Search Feature…
You control the fields that appear in a site wide advanced search form within the following admin tool:
LISTING SETUP > FIELDS TO USE > "DISPLAY IN PAGES" TAB
The following screenshot shows the columns to look at for fields that appear as fields to search by (1) and fields that appear in the search results (2):
The above screenshots specific illustrate configurations for general and site wide optional field but there are the same for multi-level, geographic region, classified specific and auction specific fields.
To make the same changes to on a per category basis you'll find those same configurations within the category specific fields to use configuration tool. That tool is explained more here
Category specific fields appear automatically in search forms when a category is selected in the advanced search form.