The certificate of sale shall be presumptive evidence in all courts in all proceedings by and against the purchaser, his representatives, heirs, and assigns, of the truth of the statements therein, of the title of the purchaser to the land therein described, and the regularity and validity of all proceedings had in reference to the sale. After two years from the record of the certificate of sale, no evidence shall be admitted in any court to rebut the presumption, unless the holder thereof shall have procured it by fraud, or had previous knowledge that it was fraudulently made or procured.