The buyer`s agent will usually make the first copy of the form as the first offer for the house for sale. Within the contract, there are several different sections to request information about how the transaction will take place. Some of the most important aspects of the sale that need to be included in the document are the price of the house, buyers/sellers and the invoice date. After agreeing on the terms of the transaction, both parties can sign the form in order to consolidate the legality of the contract. Illinois Residential`s purchase and sale agreement is a contract that binds two parties to a residential real estate transaction. Both parties, “sellers” and “buyers”, negotiate the terms of the agreement with the help of their broker, agent or broker. Once signed, the treaty is legally binding and cannot be broken. .