Tennessee Code Title 67. Taxes and Licenses § 67-6-305

There is exempt from sales or use tax the transfer, by any dealer in personal property, of any item from inventory to be used by such dealer, or the dealer's agent, or representative for demonstration or display purposes; provided, that such article of personal property shall be returned to inventory for sale in the usual course of trade within one hundred twenty (120) days; if such article of personal property is used for demonstration purposes for a period in excess of one hundred twenty (120) days, the dealer shall pay a use tax thereon for the amount that the cost of the article to the dealer exceeds the sales price of the article upon which sales tax is regularly assessed and paid when it is subsequently sold to a consumer.