Her Guinea Pigs Looked 'Miserable' in Their Cage — Her Fix Became a $71,000-a-Month Amazon Side Hustle

Bella Lin was 12 when she spent an hour a week "scraping, scrubbing and power washing" waste out of her two guinea pig cages — an experience bad enough that she started designing her own cage, first on notebook paper, then out of bricks and plastic in her backyard in Sunnyvale, California, and eventually through a factory in Hangzhou, China. That design became GuineaLoft, a small pet accessory brand she founded, built around a cage with acrylic walls and a disposable wax-coated paper bottom for easier cleaning, which she launched on Amazon in November 2022 after about a year of prototyping.

By 2024, GuineaLoft was bringing in roughly $71,000 a month in revenue, according to documents reviewed by CNBC Make It — more than double the prior year's average of $34,000 a month in revenue and about $8,600 a month in profit. Lin credits the jump largely to winning $10,000 in a pitching competition at BizWorld, a youth entrepreneurship program, which she used to buy an acrylic laser cutter that sped up production enough to keep the cages consistently in stock. The company now employs six full-time workers, though it remains Lin's side hustle alongside starting college at the University of Chicago to study economics.

GuineaLoft wasn't her first venture — she'd been selling small things since age 7, from lemonade stands to hand-knit scarves, encouraged by her father, a computer programmer who'd worked with startups and treated her business ideas seriously rather than dismissing them as kid stuff. One of those earlier ventures, TLeggings, grew out of her father asking her to research the markup on a pair of Lululemon leggings — they found similar fabric cost about $20 to produce — and went on to peak at $300,000 in revenue in 2020. Her father also connected her with the factory in China; Lin speaks Chinese but sometimes relies on him to help translate.

It took about a year to go from cage prototype to an Amazon listing of 100 units, which sold out within two weeks. Production now runs on three acrylic laser cutters, and the product line has expanded well beyond guinea pigs to hay feeders, no-drip water bottles, and cages and accessories for hamsters, rabbits, and birds — though the expansion hasn't been smooth. The hamster cage alone went through "at least five iterations" after early versions got bad reviews for letting hamsters escape.

Lin now works about 30 hours a week on the business while taking two college courses, having decided against a gap year so she can keep learning and meeting people who could help her scale it. She hasn't started paying herself a salary, relying on a scholarship and her parents to cover tuition, and instead reinvests everything back into the company, with a goal of eventually getting GuineaLoft products onto brick-and-mortar shelves and becoming a recognized small-pet brand.