If the Seahawks want to win negotiations with the Broncos, they must first accept losing Brandon Marshall. Marshall or bust is a losing strategy and the more Seattle projects a Marshall or bust front, the quicker their leverage deteriorates. In theory, Seattle started negotiations with leverage. Marshall has a poisonous relationship with Denver, right down to the city proper. Marshall wants out, and Seattle is a logical destination. If the Seahawks could convince Marshall to commit, if not formally than in spirit, to a trade to Seattle, they win leverage. Hopefully, that's what the Seahawks are attempting to do over this weekend: Woo Marshall, but not fall in love with Marshall.
The latter is how leverage can swing radically in favor of the Broncos. If Seattle begins to take Marshall for granted, begins planning around him signing, perhaps pursuing other prospects less actively, perhaps, as in the case of Nate Burleson, allowing other wide receivers to leave, increasing Seattle's need; If Seattle sets their heart on making a splash as their opportunities dwindle, then Seattle becomes locked in and may begin to fear not signing Marshall more than overspending. That can not happen.
Pete Carroll and John Schneider must understand that if Seattle does not sign Marshall, if he stays a Bronco or another team swoops in, the Seahawks can still have a very successful offseason. Seattle does not need to sign a single free agent. It has three top fifty picks and no mandate to win this season. Unless Seattle overspends for Marshall, it's in a no lose situation. The Seahawks only lose if they choose to lose.