"My advice [to parties contemplating having an LOI] is to proceed with caution before signing any such document. As a general rule (and there are exceptions), I urge the parties to go right to the final documents and "dot all of the I's and cross all of the T's," rather than go through this interim step of a letter of intent, which has many potential traps."
Buyer accepts offer and signs it, where offer acceptance is binding depends of the legal jurisdiction. For example English and common law differs slightly from American uniform commercial law on matters of offer acceptance and when performance becomes binding on an offer. The seller can also reply with a pro forma invoice. In fact a pro forma invoice can serve as quote and offer, becoming a more or less binding purchase order upon buyer acceptance and signing. Pro formas are used more in smaller FCL trades, and not in larger bulk trades.