BAFO sits at the end of a structured sourcing event. After a request for proposal and one or two clarification rounds, the buyer shortlists two or three suppliers, tells them exactly that, and asks for a final submission. The mechanism works because it converts negotiating pressure into a single decision point: each supplier knows competitors are submitting too, knows there is no second chance, and prices accordingly.

The integrity of the word "final" is the whole tool. Buyers who run a BAFO and then come back asking for one more sharpening get a predictable result: suppliers stop submitting their best number in any round, padding each offer because they expect three more. In that sense BAFO is the opposite of a reverse auction, which extracts price through visible iteration rather than a sealed last word.

A BAFO round helps when scope is fixed, the field is genuinely competitive, and differences have narrowed to commercial terms. It hurts when used to squeeze a supplier you have already decided to pick, or when your BATNA is weak and the suppliers know it. Like all competitive bidding, it only produces honest numbers when losing is a real possibility for everyone.