Letters of intent may be advanced in the world of commercial real estate. In some specific domestic markets (for example in principal to principal deals between upstream Petroleum traders and producers in the same country, or certain Joint venture projects) they may be found. But there is no underlying and supported standard international application for the Letter of Intent.
So let's sum things up: The LOI and similar documentary terms, are non standard, confusing, and lead to ambiguity. Documentary ambiguity is referred to in trade law as a condition "The Battle of the Forms" in which confusion from contradictory and ambiguous forms and documents damages the transaction. This should be avoided. To seasoned corporate traders and bankers, using terms like "Letter of Intent" is the mark of amateurs. What you properly want is an RFQ, request for quotation, from a seller or supplier. The seller may then reply to your RFQ with a quote OR full offer if they wish.