The purchaser goes to the real estate management department where the property is located to inquire about the mortgage registration. If it is verified that the developer has gone through the mortgage registration procedures 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.