It's confusing, because the terms "wholesaler" and "distributor" are often used interchangeably. However, there's a definite difference. A book wholesaler (such as Ingram or Baker & Taylor) provides warehousing and fulfillment services for bookstores. A book distributor (such as Independent Publishers' Group) does that, plus maintains a staff of sales reps who sell the distributor's list into bookstores. Wholesalers are oriented to providing services to bookstores; distributors are oriented to providing services to publishers.
If you're a publisher that's serious about getting stocked in stores, you need both a wholesaler and a distributor, or else to maintain your own sales staff. The big publishing houses have their own sales reps and distribution arrangements.
- Victoria