DeBeers managed to convince the US Federal Trade Commission to require synthetic diamond manufacturers to label their products as synthetic. But China doesn't require that. China trade practice barely distinguishes between diamonds and cubic zirconia. If you want to order diamonds from China, you have to specify HPHT (high-pressure high temperature), or CVT (carbon vapor deposition) or you'll probably get cubic zirconia.[1]
Nobody can detect better HPHT or CVT diamonds without lab equipment, anyway. Even under a microscope they look very similar. If you hit them with UV light and take a picture milliseconds after the light goes off, the fluorescence patterns are different. There's overpriced test equipment based on this fact. (Now there's a potential phone accessory - a UV flash that plugs into the phone for diamond grading, with associated app. Tiny market, though.)
Nobody can detect better HPHT or CVT diamonds without lab equipment, anyway. Even under a microscope they look very similar. If you hit them with UV light and take a picture milliseconds after the light goes off, the fluorescence patterns are different. There's overpriced test equipment based on this fact. (Now there's a potential phone accessory - a UV flash that plugs into the phone for diamond grading, with associated app. Tiny market, though.)
[1] https://www.alibaba.com/product-detail/High-quality-white-hp...