While both the buyer and seller must sign the document, a notary and/or witnesses are not always required. It is still prudent to have it notarized because it prevents either party from claiming that they never signed the document. A notary ensures that the contract is legally binding and can help avoid a messy dispute down the line. It may seem like an inconvenient expense, but the guarantee of a notary increases the integrity of the agreement and provides insurance should things not go to plan.