An exempt sale without proof is a taxable sale; Sundry requests the proof the law asks for, checks every required point, and treats a sale as exempt only with a verified proof in date at the sale.

Dana My client says this sale is exempt.
Sal An exempt sale without proof is a taxable sale.
Sal So Sundry requests the proof the law asks for, reads it, and checks every required point against what the buyer submitted.
Sal A sale is exempt on the return only when a verified proof is in date at the sale.