The buyer will need the executed sales agreement to obtain financing and it is always better to put an offer in writing.
For Sale by Owner Checklist
Before a buyer signs the sales agreement, you should provide the buyer with a seller's disclosure.
You will want the buyer to give you a pre-approval letter from a lending institution to prove to you that they are able to purchase your property.
Abstract Company or a Real Estate Attorney
Both you and the buyer will need to obtain an attorney or abstract company to handle the exchange of money and the legal documents. As the seller you are required to have a deed prepared, along with other seller documents. The buyer will also need to have representation as most lending institutions require title insurance. The buyer and seller can agree to have the same Abstract Company or Attorney handle the closing on their behalf.