When I was 19 years old, I lucked into a job working in a local bank (where I would continue working for 20 years). One of my first duties was rolling coin in the bank vault. I used a motorized roller that required manual operation (holding an empty paper coin roll inside a plastic tube as it filled with coins). Some of the coins we received from the Federal Reserve were circulated and sometimes they were fresh from the mint.

One day in 1975, I was rolling some new pennies from the Denver mint when my coin rolling machine started jamming. I discovered that there were some misstruck coins that would not flow through the machinery. Error collectors call these "cuds" and they're caused when part of the die breaks off. I found two different varieties, minted at different stages of the break. I picked 200+ bad coins out of the hopper and purchased them from the bank.

A few months later I sold about half of them at a local coin show and put the rest away. When eBay started up I began listing them one by one every few months, taking a break when the market reached a saturation point. They've sold for anywhere from $15 to $80, which isn't a bad return on their original cost of $.01.

BTW, I just listed one on eBay if you'd like to add one to your collection.