Best judgment assessment: tax authority may value taxable services after records are sought and a hearing to fix tax payable. Best judgment assessment authorises the Central Excise Officer to require production of accounts and other evidence, consider all available material, and, after giving the person an opportunity of being heard, make a written assessment of the value of taxable service to the best of his judgment and determine the sum payable or refundable where the assessee fails to furnish a return or assess tax in accordance with the Chapter or rules.