sir @pwuser156346747849 if you have the documentation as buyer's cnic, deal date as in delivery receipt with vehicle regn engine & chassis number, sale deed, and transfer letter copy you need not to worry. as pre-caution you may speak to buyer over the phone for transfer of vehicle so that you do not get benefit of withholding tax at time of annual tax payment. that may trigger his interest as to why benefit goes in your favor for his payment. as 2ndry measure you may write a letter to respective registration authority of vehicle sale with copy of delivery receipt and buyer's cnic. Send that letter with attachments by TCS and hold the copy of TCS dispatch receipt.