Some businesses have an inauspicious start; Eric Fanelli's has a particularly unfortunate one: His cat peed on his hockey gear. But the search to replace his ruined paraphernalia would lead the Connecticut dad to launch a side hustle that now nets him over $100,000 a year.

It started with the hockey pants. Fanelli came across a used pair from the University of Connecticut's team at a local sports store. At $65, they were half the price of new ones — and arguably cooler.