72 Pa. Stat. § 2644
The mercantile appraiser shall leave with the vender or dealer a written or printed notice, to be prepared and furnished by the Department of Revenue, specifying the classification and the amount of license money to be paid by such person to this State and also the time and place, when and where an appeal will be held as required by law. Any vender or dealer subject to the provisions of this act who is dissatisfied with the rating so made by the mercantile appraiser shall have the right of appealing to the mercantile appraiser and county treasurer, who are required to hear him on the day so fixed by the mercantile appraiser and county treasurer for the appeal. If the vender or dealer is still dissatisfied with the finding of the county treasurer and mercantile appraiser or board of appraisers in reference to the proper classification of the said vender or dealer, he shall have the right of appeal within the time prescribed by law to the court of common pleas of the proper county, which appeal the said court is required to hear and determine within twenty days after such appeal shall be taken, or at the next sitting thereof. If any person fails to attend the appeal before the county treasurer and mercantile appraiser, board of appraisers or the court, he shall not thereafter be permitted in a suit for the recovery of said mercantile license tax to set up as a defense either that he is not a vender of or dealer in goods, wares, and merchandise, or any other ground of defense which might have been heard and determined either by the said county treasurer and mercantile appraiser, board of appraisers, or the court of common pleas on appeal, as aforesaid.
72 P.S. § 2644