Welcome to the forum.
A five screw .44 Mag will have a large sideplate screw just below the rear sight on the right side of the frame. A four screw will lack the large sideplate screw, but will still have the screw on the front of the triggerguard where it meets the frame. A three screw will have none of the above.
There's a lot more to evaluating a .44 Magnum than counting the screws. The accessories, the finish, the barrel length, the revision level, the overall condition and the grips can have a tremendous effect on value.
Good luck. If you get it, we want pictures!