I have played with a fake controller and there's a visible difference in how the original feels and plays.. The fake one is not as sharp and swift in movement and may be slow and laggy at times. The 3k price is on the expensive side and but worth it.. I myself bought one from Sony Store for 3k.
Only original. The analog sticks on the fake ones tend to get stuck. It simply doesn't spring back into neutral position often.
Second thing, the tactile feel.