Place of supply rules: services require distinct treatment due to intangibility and variable location of performance compared to goods. Services are intangible and therefore create distinctive difficulties for determining the place of supply: delivery modes can change, billing or contract locations can be altered, and provider, recipient and supply may lack a tangible trail. A service element may relate to multiple locations, recipients may be mobile during receipt, and service methods continually evolve, all of which justify specific place of supply provisions for services to address ascertainability, prevent suppression, and allocate taxing rights.