A lot of composite bats look more like "textured snakeskin" on the inside due to how the composite fibers are woven together. Check out
this video to get a good idea as to how composite softball bats are made.
Look for a few things: does it look like someone went at it with a wire brush on a power drill? Are the inner walls of the bat REALLY smooth?
How about the end cap? Does it look like a crappy epoxy job like this?
Look at the following picture. You can see how the bat was shaved only so far, and how you can see the "snakeskin" I'd mentioned earlier down towards the taper.
Also, look at the end cap to see if anything "unnatural" has been added to it: BBs, weights, etc.
But be careful. Manufacturers, naturally, will vary their techniques in weaving the fibers, and just because a bat is smooth on the inside does not mean it's shaved.
In ASA, it's standard procedure for the umpire to collect all pieces of the broken bat and confiscate them for a more official evaluation. Not sure how NFHS handles it.