Legal analysis: It is recommended that the letter of guarantee be witnessed by a lawyer, as long as it is a written document signed by both parties, and it is signed voluntarily by both parties. It can be used as a valid basis in law.

Legal basis: "Interpretation of the Supreme People's Court on the Application of the Civil Procedure Law of the People's Republic of China" Article 110 If the People's Court deems it necessary, it may require the parties to appear in court in person , to be questioned about the relevant facts of the case. Before questioning the person concerned, he or she may be asked to sign a bond.

The letter of guarantee shall state the truthful statements and willingness to accept punishment if any false statements are made. The parties concerned shall sign or seal the guarantee letter.

If a party who bears the burden of producing evidence refuses to appear in court, refuses to be questioned, or refuses to sign a letter of guarantee, and the facts to be proved lack other evidence, the people's court will not recognize the facts claimed by him.