A first question you might ask when considering hiring an indexer is, why do you need an index?
Short answers: If you want your readers to be able to easily access the information in your book, then you need a good index. If you want a good index, you need to hire a professional indexer.
A professional indexer knows how to catalogue the information in your book into easy-to-follow topics and listing of subject matter. A professional indexer is a bit of a mind reader, able to intuit what your readers will want to search in your book, and how they might go about searching for those topics.
Picture a map of an city’s train lines, with colors indicating each train, and the lines tracing the route of each train. It’s the same for indexes: each color indicates an individual thread, and the lines trace that thread through the pages of the book, showing even where topics interconnect. A good index is a detailed map of the book.
Indexers bring fresh eyes to the subject matter, sometimes finding connections that you as the author might have missed. Because indexers are farther removed from the subject, they can bring a new perspective to the subject matter.
Indexing is a deceptive endeavor, seemingly simple, but to truly appreciate an index, one must understand the intuition, attention to detail, and constitutional organizational skills that are part and parcel of the task.
Why hire an indexer? Perfect answer. Because you want to enhance the value of your book.