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.
However, sometimes one of the parties prepares a document believing it to be a valid and enforceable agreement only to find, after expensive litigation, that it was not a binding agreement at all but merely a non_binding, non_enforceable agreement to agree, letter of intent."