It has legal effect. For details about whether it is legal or not, please refer to the "Contract Law" below.
The sales contract is a civil legal act between both parties. As long as both parties sign it legally and voluntarily, it is valid.
Regarding invalid contracts, the Contract Law has special provisions:
(1) One party concludes the contract by means of fraud or coercion, harming national interests;
(2) Malicious collusion to harm the interests of the country, the collective or a third party;
(3) Covering up illegal purposes in legal forms;
(4) Harming social welfare*** Interests;
(5) Violation of mandatory provisions of laws and administrative regulations.
The above five situations are invalid contracts expressly stipulated in the law. Contracts other than these are valid if signed by both parties.