Where on a Black Widow is the serial number located? I am buying one and the guy can't find it. So unless it is under the limbs it must be a fake right?

Take the limbs off & look on the limb butt.

Is that where they always are, or are they different? I just want to make sure I am not getting a fake.

That is where they always are. Gotta take the limb off and look at the butt end. The serial number also tells the year. example would be like 97123 means the bow was made in 97.