1. If it is verified that the developer has gone through the mortgage registration formalities for the house purchased by the purchaser, and the mortgage behavior occurred before the purchaser and the developer signed the purchase contract, according to the law, the developer can only transfer the house as collateral to the purchaser with the written consent of the mortgagee (that is, the loan bank), otherwise, the transfer behavior is invalid. In this case, the commercial housing sales contract signed by the purchaser and the developer is invalid, and the purchaser has the right to ask the developer to return the paid purchase price and compensate the losses such as interest.

2. If the mortgage behavior of the developer is verified to be true, the buyer can ask the developer to bear the losses that may be caused by the mortgage of the real estate after signing the commercial housing sales contract with the developer, such as the buyer failing to handle the property right certificate on time. Of course, since the purchaser has obtained the usufructuary right after signing the commercial housing sales contract with the developer, the developer has no right to mortgage the house in his own name. Therefore, the purchaser can ask the developer to release the purchased house within a time limit. Otherwise, the developer can be required to bear tort liability and claim compensation for the economic losses suffered.