The difference between a Regular frame and a Featherweight is that the lug on a Regular frame is 1 3/16" long x 1/2" wide. The Featherweight is 11/16" long x 3/8" wide. Obviously we can't see the length in the picture. The other sure way is that a Featherweight has 3 screws holding the sideplates on, 2 on the one side and 1 on the other, whereas a Regular frame only has 1 screw in the sideplate. This one here only has 1 screw holding the sideplates on, and that is the opposite side we see. Plus the picture is not a good one because the hump on the sideplate looks too exaggerated and is to short in length. It just happens to be that way because of the angle of the picture. So if indeed it is a 20 ga. Regular frame and the barrels weren't altered, it is definelty a good find and a steal at that price.
We really need some close-up pictures of the receiver and forend and the the markings on the watertable. Unfortuately, it was stated that the gun was sold. it also has a recoil pad on it. Why?, with the short barrels it could have been made for a younger person or a woman. Unless the original poster can get us the serial number, we won't know.
