It shall be the duty of the auditor general to charge the treasurers of the said cities or counties with the amount payable by the several persons mentioned in said lists, from the payment of which the said treasurers shall be exonerated only by procuring satisfactory evidence to the accounting department that the person or persons so returned were not wholesale dealers and retailers of foreign merchandise or liquors, according to the true intent and meaning of this act, or that it was impracticable to collect and recover the same.
72 P.S. § 2834