The library must provide the new vendor with a clean, accurate list of titles that are being transferred along with the latest payment data. Multiple or partial lists may only serve to confuse the new vendor. Memberships, combined subscriptions, and multiple copies require special attention. Libraries select vendors in different ways. Some states require that you go out on bid.
Vendors have standard proposals that they can customize.
They also do RFPs and RFIs. Because of the time involved, vendors don't appreciate being sent 10-15 page RFPs, if they don't have a realistic chance of getting the business. The library needs to determine which services are truly needed. As far as pricing goes, vendors receive a discount or commission from the publisher in exchange for handling its titles. The discount varies according to publisher and discipline.