An exporter with access to futures trading who sells PTBF buyer's call can lock in their final price ahead of the buyer's fixation in one of two ways.Example One
Example Two
Both examples yield the same result because the assumption is that the differential (price difference between futures and physicals) remained the same. In neither case does the direction or extent of the general market movement matter, but had there been an unexpected shortage of Mexican Prime then of course the differential would have moved against the exporter and they could have lost money because of this.This basis or differential risk exists regardless of whether one sells PTBF buyer's call or seller's call - it cannot be hedged in the futures market (although, given the huge number of PTBF trades it is not inconceivable that this could change in the future).