1. The car purchase contract is valid only if it is signed and not stamped. Unless otherwise agreed by the parties, a contract is valid only if it is signed and not sealed. If the parties enter into a contract in the form of a contract, the contract shall be established when the parties sign, seal or press their fingerprints. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it.

2. Legal basis: Article 490th of the Civil Code of People's Republic of China (PRC).

If the parties enter into a contract in the form of a contract, the contract shall be established when the parties sign, seal or press their fingerprints. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it. A contract shall be concluded in written form as stipulated by laws, administrative regulations or agreed by the parties. If the parties do not do this in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.

Second, what should I do if I pay a deposit for buying a car and sign a contract and regret it?

I paid a deposit for buying a car, signed a contract and regretted it. I don't refund the deposit. Buyer's regret is a personal factor. If the buyer regrets not performing the debt or the performance of the debt does not conform to the agreement, he has no right to demand the return of the deposit. According to the law, the parties may agree that one party shall pay a deposit to the other party as a guarantee for the creditor's rights. The deposit contract is established when the deposit is actually paid. The amount of the deposit shall be agreed by the parties; However, it shall not exceed 20% of the subject matter of the main contract, and the excess shall not have the effect of deposit. If the actual amount of deposit paid is more than or less than the agreed amount, it shall be deemed as a change of the agreed amount of deposit.