7. Where goods on which sales tax or excise tax has been paid under the Act are exported without having been used in Canada, a refund of the taxes so paid or a deduction from future taxes payable may be granted,

• (a) if evidence of payment of the tax on the purchase of the goods, in the case of domestic goods, or

• (b) if evidence of payment of the tax on the importation of the goods in the form of a receipted copy of the original import entry, in the case of goods imported into Canada,

is maintained on file by the exporter for examination by officers of the Department and evidence satisfactory to the Minister is produced to establish that the goods have been exported from Canada.