From Self-Publishing Resources:
Although the terms “wholesaler” and “distributor” are frequently used interchangeably . . . there is a difference. Wholesalers have no sales reps; they simply fill your book orders and actually buy your book outright. Distributors work on a consignment basis, paying you for sales ninety days after they have been made.
Baker & Taylor is the country’s oldest and largest library wholesaler. B&T has over the last several years dramatically increased its sales to bookstores, as well. Corporate headquarters is located in Charlotte, North Carolina, and there are branches around the country as well as in in the UK. The wholesaler’s file system lists more than a million titles, CDs, and DVDs.
To get on its database, B&T requires a $125 fee to establish new vendors, and it aggressively courts small publishers.
. . . .
Just as KFC’s success attracted Boston Market and other contenders, there are more large book wholesalers. Headquartered outside of Nashville, Tennessee, Ingram is another huge wholesaler. Its forte is fast delivery of popular books to bookstores. As of BookExpo America 2001, however, Ingram announced it is no longer dealing directly with publishers of less than ten titles.
Link to the rest at Self-Publishing Resources