If you and the seller cannot come to an agreement, you may be able to file a lawsuit against the seller.
The Texas Deceptive Trade Practices Act (DTPA) prohibits sellers from using "false, misleading, or deceptive acts or practices" when making a sale. These laws are in Chapter 17 of the Texas Business and Commerce Code. See Section 17.46 for a list of unlawful acts.
If the seller failed to disclose a major issue or lied about the car’s condition, the buyer may be able to file a lawsuit under the DTPA.
You can learn more about these laws in the library’s Consumer Protection guide.
The law can be complex, so you may wish to talk to an attorney before taking any action. For more information on finding an attorney, please see the library's Legal Help page.