Section 372.050 - "Retail sale" and "sale at retail" defined1. "Retail sale" or "sale at retail" means a sale for any purpose other than resale in the regular course of business of tangible personal property.2. The delivery in this State of tangible personal property by an owner or former owner thereof or by a factor, or agent of such owner, former owner or factor, if the delivery is to a consumer or person for redelivery to a consumer, pursuant to a retail sale made by a retailer not engaged in business in this State, is a retail sale in this State by the person making the delivery. He shall include the retail selling price of the property in his gross receipts.