Frequently under the old style of operating, there is no contract or formal agreement and often the players are all different. The agent staff has changed, the sales person is gone, or the library staff is in different positions. Usually no one is around who remembers the full details of the original sales presentation. While no one wants to go through the formal bidding process, it is still a good idea to have a letter of agreement in place and to monitor the terms and conditions. Have a fixed period of time that the agreement covers.
Some agents charge a penalty for single orders.
One Correction In Billing per title per year is enough. Some agents charge extra for GPO or Neodata. Some vendors have the computer calculate the service charge and a target margin is maintained. Any change in mix of titles or decreases in publisher discount will result in an automatic service charge increase. Check out the service charge on credits.