Had a rear wheel lock up at 20 mph in Portland, and the culprit was something I never inspect
Last Tuesday I was riding home across the Broadway bridge in Portland when my rear wheel just froze, and the bike skidded sideways before I got it stopped. A cone on my rear hub had backed out enough to let the axle shift, which jammed the cassette against the frame. I pulled the wheel off on the sidewalk and found the locknut loose enough that I could spin it with two fingers. Now I check both cones and locknuts whenever a bike comes in, not just when the wheel feels wobbly. How often do you all actually pull a cassette just to look at the hub, or do you wait for the customer to say something feels off?