Does anyone know what texas bases the tax value on for cars older than 25 years? Under 25...they use the standard presumptive value and not the selling cost. I am buying a 1987 car. Edit: might have found an answer in this handbook. Private-Party Sale or Seller’s Identity is Not Documented For a Motor Vehicle Fewer than 25 Years Old • Use the SPV procedure, which includes comparing the price to other documentation (e.g., bill of sale, canceled check), if available. • If the SPV is not available, require an appraisal on Form 14-128. For a Motor Vehicle 25 Years Old or Older • Use a seller-signed bill of sale. • If a signed bill of sale is not available, then require an appraisal from a dealer, insurance adjuster or at the discretion of the county TAC, someone who would have special knowledge of the vehicle’s value.