I'm not a certified gun appraisal person, but I do know that new Sako Hunters usually sell for about $850 or so. As such, the price you mentioned seems fair as it is a used gun, but then again, that depends on the condition of the gun. If it is in 99.9% condition, then $675 does seem fair.
I would try and get it for about $600, which is reasonable.
Zachary