On the one hand, the provisions of the Marriage Law and its judicial interpretation are unclear, and on the other hand, people have different understandings of the real right registration system. Case 1: Li Minghe Wang Hong is husband and wife. After their marriage, they bought a house and registered it in the name of Li Ming. Later, Li Minghe Zhao Gang signed a real estate sales contract to sell the real estate. After the house price rose, Li Ming told Zhao Gang that the purchase and sale of real estate was not approved by Wang Hong, so the purchase and sale contract was invalid. Analysis: The Property Law stipulates that real estate will take effect after registration, and the publicity of real estate has credibility. Although the house is the property of Li Minghe Wang Hong, it is only registered in the name of Li Ming, so Zhao Gang has reason to think that only Li Ming is the property owner and the sales contract should be valid. Of course, if Li Ming wants to divorce Wang Hong and colludes with Zhao Gang to sign a false sales contract and sell it to Zhao Gang to transfer his property, the sales contract is invalid. Case 2: Guo Hua and Liu Xia bought a house after they got married, and both of them were registered as property owners. Later, Guo Hua signed a real estate sales contract with Zhang Shaogang behind Liu Xia's back and sold the house. After Liu Xia was informed, she sued the court and asked to confirm that the sales contract was invalid. Analysis: If the buyer only signs a real estate sales contract with one of the registered couples, the effectiveness of the contract depends on the following circumstances: 1. If other property owners approve or have evidence to show their intention to sell, the contract is valid; 2. If another property owner fails to ratify it, and there is no evidence that he intends to sell it, the contract is invalid. Therefore, Zhang Shaogang must have evidence to prove that Liu Xia agrees to sell, otherwise the contract will be invalid. There is a theory of "family agency" in civil law. The right of family agency refers to the right of husband and wife to represent the other spouse when they have certain legal acts with a third person due to daily family affairs. The so-called "daily housework" is usually understood as daily affairs closely related to family life, such as purchasing necessary daily necessities, medical services, cultural consumption, children's education and so on. However, real estate occupies an important position in family property, and buying and selling real estate obviously does not belong to the daily family affairs, so Guo Hua cannot sell real estate on behalf of Liu Xia just because he and Liu Xia are husband and wife. Therefore, the real estate registered as husband and wife is only valid if both parties have the will to sell it together. Case 3: Gong Li signed a real estate sales contract with Chen Mei, stipulating that Gong Li would buy a house in the name of Chen Mei and Chen Mei's husband Liu Zhihua, but the house price rose rapidly. Chen Mei suddenly proposed to raise the price, otherwise she wouldn't sell it, and Gong Li refused to add money. Unexpectedly, it was not long before Gong Li and Chen Mei were brought to court by Liu Zhihua. Liu Zhihua said in the complaint that Chen Mei sold the property they enjoyed behind his back and demanded that the sales contract be invalid. Analysis: According to the provisions of the Marriage Law, if there is no special agreement, the property purchased during the marriage relationship should be recognized as the joint property of husband and wife, that is, whether it is registered as one person or two people, it should be recognized as the joint property of husband and wife. As mentioned above, if there is no evidence that Liu Zhihua agrees to sell, then the sales contract is invalid. However, the invalidity of the contract does not mean that there is no legal responsibility. According to the provisions of the contract law, after the contract is invalid, the party at fault shall compensate the other party for the losses suffered as a result. If both parties are at fault, they shall bear their respective responsibilities. Therefore, Gong demanded compensation for his losses, including the price difference after the house price rose. Case 4: Qian Qiang signed an intermediary agreement with Liu Ming and Sun Li, stipulating that Qian Qiang would purchase the real estate under the names of Liu Ming and Sun Li. When signing the formal sales contract, Sun Li didn't attend the signing because of a business trip. Only Liu Ming signed the contract, and Sun Li's name was signed by Liu Ming. Who knows that the house price has gone up, and Liu Ming regrets that the house has been sold cheaply, saying that there is no Sun Li's signature on the formal contract, so the contract is invalid. Analysis: Although Sun Li did not sign a sales contract, Sun Li has signed an intermediary agreement, which shows that she agrees to sell the property, which constitutes an agency by estoppel in the contract law. If the buyer really has reason to believe that the signatory has the agency right of the other party, the contract shall be deemed valid, otherwise it shall be deemed invalid. For example, if there is evidence that the other party entrusts an intermediary to list, negotiate together, sign an intermediary agreement, and receive the down payment or house payment, it can be said that the other party agrees to sell, and then the contract can be considered valid.