If the seller or CSP has not obtained an exemption certificate or all relevant data elements as provided by the Tax Commission, the seller may, within one hundred twenty (120) days subsequent to a request for substantiation, either prove that the transaction was not subject to tax by other means or obtain a fully completed exemption certificate from the purchaser, taken in good faith.
The Tax Commission shall relieve a seller or CSP of the tax otherwise applicable if it obtains a blanket exemption certificate for a purchaser with which the seller has a recurring business relationship. The Tax Commission shall not request from the seller or CSP renewal of blanket certificates or updates of exemption certificate information or data elements when there is a recurring business relationship between the buyer and seller. For purposes of this section, a recurring business relationship exists when a period of no more than twelve (12) months elapses between sales transactions.
Okla. Stat. tit. 68, § 1361