In all public sales of land hereafter made by the treasurer or commissioners of the several counties of this commonwealth, in pursuance of the laws of this commonwealth the rule of caveat emptor shall apply, except in cases of double assessment, or where the taxes on which the sale is made shall have been previously paid, or where the lands do not lie within the county; and neither said treasurer nor commissioners shall be required to refund the purchase money, costs or taxes paid upon any tract or tracts of land so sold as aforesaid.
72 P.S. § 5931