A.R.S. § 42-5022: Burden of proving sale not at retail

The burden of proving that a sale of tangible personal property was not a sale at retail shall be on the person who made the sale, unless either:

1. The person has taken from the purchaser a certificate signed by and bearing the name and address of the purchaser that the property was purchased for resale in the ordinary course of business and that he has a valid license, with the number thereof, to sell the kind of property purchased.

2. The person is exempt from the requirement of a certificate pursuant to section 42-5009, subsection N.