The trading of concessions including price reductions, between supplier and customer, in an attempt to shape a supply contract (sale) so that it is acceptable to both supplier and customer, negotiations can last a few minutes or even a few years, although generally it's down to one or two meetings and one or two exchanges of correspondence, ideally, from the seller's point of view, negotiation must only commence when the sale has been agreed in principle, and conditionally upon satisfactory negotiation, however many sales people fall into the trap set by most buyers - intentionally or otherwise - of starting to negotiate before the selling process have even commenced.