I use an orbital palm sander for the final tillering of the fades, it gets rid of any washboard in the grain and makes a nice transition from the limb to the fade.
One common mistake is to scrape the fade from handle to limb which will almost cause a dip at the juncture of the fade and the limb.
I saw a really nice BBO the other day that was obviously made by an experienced bowyer, it had broken at the bottom of the fade. One sideways glance showed the bowyer had made a fatal dip at the end of the fade instead of a smooth transition.