Legal analysis: Generally speaking, the letter of commitment does not need witnesses and guarantors, but only the signature and handprint of the promisor, but it is better to have witnesses. Generally, the guarantor has the right of defense before litigation, that is, before the main contract dispute has been tried or arbitrated, and the debtor's property has not been enforced according to law, the guarantor can refuse to undertake the guarantee responsibility to the creditor.

Legal basis: Article 687 of the Civil Code of People's Republic of China (PRC) stipulates in the suretyship contract that when the debtor fails to perform the debt, the surety shall bear the suretyship responsibility, which is a general suretyship. The guarantor of a general guarantee has the right to refuse to undertake the guarantee liability to the creditor before the main contract dispute has been tried or arbitrated and the debtor's property has been enforced according to law, except in one of the following circumstances:

(1) The debtor's whereabouts are unknown and there is no property available for execution;

(2) The people's court has accepted the bankruptcy case of the debtor;

(3) The creditor has evidence to prove that the debtor's property is insufficient to perform all debts or cannot perform debts;

(4) The Guarantor waives the rights stipulated in this clause in writing.