I run my thumbnail all the way around each end of the shaft, by both the nock and insert, checking for small, hard to see cracks. Then I flex the shaft and hold it that way while I roll it in my fingers, looking for a spot that suddenly flexes more, or to see if there are any cracks. At the same time I'm listening to see if the shaft makes any cracking noises. If it passes those tests, it goes in the quiver. If not, I remove the nock and point and toss it in the busted arrow bucket to use for tomato stakes.

If you've got an arrow with a nock that used to fit well but is suddenly loose, then that's a good tip-off that you've got an arrow that's cracked at the nock end.