I bought a 6+7-storey (multi-storey) auction house. At the time of delivery, the developer said that the attic area had increased by 17 square meters and asked me to return it.

It depends on how you signed the original contract. According to the general principle, it should be handled in the following way. When the absolute error ratio between the construction area and the interior construction area exceeds 3%, the buyer has the right to return the house. If the buyer refuses to return the house, if the measured construction area is larger than the predicted construction area, the buyer shall make up the house price for the part with the error ratio of the construction area within 3% (including 3%); More than 3% of the house price shall be borne by the seller, and the property rights shall be owned by the buyer. When the measured construction area is less than the construction area agreed in the contract, the house price of the part with the absolute error ratio of the construction area within 3% (including 3%) shall be returned by the seller to the buyer; The absolute value of the house price exceeding 3% shall be returned by the seller to the buyer twice. So ... I think your 17 square meter definitely exceeds the error of 3%, and you should claim compensation from the developer. I hope I can help you! The answers come from: "Baidu real estate exchange group" and "commercial financial management knows thousands of households", so stay tuned!