Specifications include, but are not limited to: The successful vendor must agree to mark shipments and invoices with a purchase order. Shipment must be delivered prepaid to the Center location indicated on the purchase order, unless otherwise specified. Packing lists are to accompany the shipment in a container/carton properly marked as PACKING LIST for distribution to the Center with the material. The successful vendor shall agree that all items shipped in error, such as incorrect colors, etc. will be picked up by the vendor and the items will be replaced at no extra cost. Notification of concealed shortages reported by the Center are to be accepted by the vendor and items delivered at no cost to the Center. No charge packing list marked with the applicable purchase order number shall be enclosed with each “no charge” shipment. Specifications are for unknown quantities of items to be purchased on an “as needed” basis.