(a) All gross sales of a retailer are subject to the tax imposed by this article until the contrary is established. The burden of proving that a sale of tangible personal property is not a sale at retail is upon the person who makes the sale unless he takes from the purchaser a certificate stating that the property is purchased for resale.

(b) The certificate relieves the seller from the burden of proof as provided in subsection (a) of this Code section only if taken in good faith from a person who:

(1) Is engaged in the business of selling tangible personal property;

(2) Holds the permit provided for in this article; and

(3) At the time of purchasing the tangible personal property, intends to sell it in the regular course of business or is unable to ascertain at the time of purchase whether the property will be sold or will be used for some other purpose.

(c) The certificate stating that the property is purchased for resale shall:

(1) Be signed by and bear the name and address of the purchaser;

(2) Indicate the number of the permit issued to the purchaser; and

(3) Indicate the general character of the tangible personal property sold by the purchaser in the regular course of business.