If the conditions above are met it is immaterial (1) that the contract of sale is closed by acceptance outside the State or (2) that the contract is made before the property is brought into the State.
Delivery is held to have taken place in this State (1) when physical possession of the tangible personal property is actually transferred to the purchaser or the purchaser's designee within this State, or (2) when the tangible personal property is placed in the mails at a point outside this State and directed to the purchaser or the purchaser's designee in this State or (3) when the tangible personal property is placed on board a carrier at a point outside this State (regardless of shipping terms) and directed to the purchaser or the purchaser's designee in this State.
The term "engaged or continuing within this State in the business of selling tangible personal property at retail" as used in this regulation shall have the same meaning as the term "retailer maintaining a place of business in this State" as defined in Code Section 12-36-80.
S.C. Code Regs. § 117-334.1