Increase your chances of getting a nonfiction publishing agent by labeling your book accurately in your query letter. If you use the correct category description, you're much more likely to get the right publishing agents offering representation. And, in some cases, you can use more than one category description, allowing you to query a greater number of book agents.
For example, we are currently coaching a woman who has written a nonfiction book about her and her military father. Though the book is memoir more than anything else, calling it memoir is not our only option. Publishing agents who say they represent one or more of the following book genres might also be interested: Biography, Narrative Nonfiction, Nonfiction History, Nonfiction Military/War, Upmarket Nonfiction, Multicultural Nonfiction, and General Nonfiction.
Make sure you understand the book genres relevant to your book. Doing so will allow you to categorize your book in the best way, but it might also let you use more than one label, depending who you are querying--and that can allow you to query more book agents.