I buy earrings on there all the time. The company is owned by Alibaba, a company that SoftBank (which in turn owns Sprint) owns about a third of. A few words of advice:
1. Everything with a recognizable name brand is counterfeit, and there's a wide range in quality, so only buy items where you don't care if it's fake. (Clothing/textiles and jewelry are fine, but I wouldn't recommend tech).
2. Most items take about a month to arrive unless you pay for express shipping
3. If they get suspicious (either because you order too much or use pre-paid credit cards), they have a shit verification process that requires a photocopy of your credit card, ID, etc. If you refuse, they'll continue to cancel every order you place (although it's easy to get around by creating a new account).
4. Lastly, when you place an order, your money will go into an escrow account for a period of time (pre-determined by the seller); the seller doesn't get paid until the time expires or you confirm you've received the item. If you have a problem, make sure you file a complaint within this window, or ask for an extension if you still haven't received the item. Otherwise, you're out of luck.
In short, yes it's legit, but it's sketchy nonetheless.