Ingram Book and Ingram Entertainment are closely related companies (both are part of the Ingram family dynasty in Nashville, which is kind of a big deal -- if you live in Nashville.)
Ingram Book is one of if not the largest distributors of books in the world. They are well-known in the book business as being the primary supplier for many brick-and-mortar stores and chains, most notably Barnes & Nobles, whose guidelines for authors and publishers include the requirement that if that publisher wants their books on B&N shelves, then the book has to be listed in the Ingram catalogue.
You can expect a level of service and selection from them that makes most other wholesalers look like they're run out of some guy's garage. Prices are ... kind of not so great, but wholesale book pricing is generally almost as bad as video games and media, no matter where you buy it.