Intermediary services defined as facilitation between parties; taxable when provider arranges supplies without acting on own account. Intermediary services are those that arrange or facilitate the supply of goods, services or securities between two or more persons while not supplying the main goods or services on their own account; essential indicia include lack of material alteration of the main supply, separable identifiable remuneration (such as commission), documentary authority to act for the principal, and the existence of distinct main and ancillary supplies, whereas persons supplying the main service on their own account, principal-to-principal suppliers, and subcontractors performing the main service are excluded.