1. Expertise: Dong Yuying has expertise in jewelry appraisal. Knowing the different types, qualities and prices of gems can help him choose high-quality jewelry and sell it at competitive prices.

2. Market demand: As a kind of luxury goods and fashion accessories, jewelry has always had a stable demand in the market. With consumers' pursuit of fashion and individuality, there are more and more opportunities in the jewelry market, so Dong Yuying sells jewelry.