I've been using aliexpress to purchase jewelry and children's clothing for the most part. Some orders have been problematic, and Aliexpress does absolutely NOTHING to help the buyer.
So my advice is buy very small quantities until the seller proves their trustworthiness. If you only buy $10-$15 at a time, you don't have that much to lose.
It is true what everyone else here says, that Aliexpress's "buyer protection" is bullshit. It really is.
So just be careful, don't buy high ticket items from unknown sellers, and keep in mind that you get what you pay for in the sense that quality and service matches the price (and sometimes, you pay and don't get anything at all!).