Even taken at their word, it doesn't change the fact that they are using documentary procedures that are unusual, and abnormal. Contact any business college, or speak to established traders or people working for large multinational corporations. Talk directly to international bankers on this.
So you see, the response requested is indicated in the very form and name of the document itself. The Letter of Intent has no established place in International trade law. Where they are used _ rarely _ is in some small niche internal markets and trades. The RFQ, Request for Quotation, a standard protocol in the business world, is what most brokers actually want when they err in using an LOI.