Sellers can determine which categories contain the most matching items by using the getCategorySuggestions method of the Taxonomy API and comparing the values returned in the categorySuggestions array. The suggested categories returned in this array are sorted in order of eBay's confidence of the relevance of each category.
For complete information about the getCategorySuggestions method, refer to the getCategorySuggestions reference documentation.
Specify a query for suggested categories
The query, defined by the q parameter, is a search string that describes the item being offered for sale. The string format is free form, and can contain any combination of phrases or keywords. eBay will parse the string and return suggested categories for the item.