Vent: A customer's old Raleigh three-speed taught me about cottered cranks

This guy brought in a 1970s Raleigh with a wobbly crank, and I was about to tell him it was toast. He said, 'Just tap the cotters, son, they walk out over time.' I'd never actually seen that fix in real life, just read about it. Sure enough, a few light taps with a hammer and punch tightened it right up. It's wild how much old-school knowledge is still out there. Anyone have a good trick for removing a really stuck cotter pin without damaging the crank arm?