Texas Tax Code - TAX § 152.044. Payment by Seller

(a) If the comptroller on an audit of the records of a seller finds that the amount of tax due was incorrectly reported on a joint statement and that the amount of tax paid was less than the amount due, the seller and purchaser are jointly and severally liable for the amount of the tax determined to be due.

(b) The comptroller shall ascertain compliance with the terms of this section.  If the comptroller on an audit of the records of a motor vehicle dealer finds that the documents necessary to title and register a motor vehicle in the name of the purchaser of the motor vehicle have not been executed and delivered to the tax assessor-collector, together with tax due, if any, the motor vehicle dealer is liable for the amount of the tax due, plus penalty and interest, if any.