First of all look at the price... second look at the minimum order quantity... and look at payment options
If the price is too low its not going to be genuine.... large genuine manufacturing companies who make reputable items don't usually offer small order buying.... if its cash or transfer only payment its probably fake... that does not mean you wont get the items, it just means when/if you do they will look genuine but probably be fake but not necessarily made in China... A guy in Bangkok used to have a stall outside the Rolex shop... his pitch was "look in the window and I will get you a copy" he could supply copies from China/Japan/Taiwan/Thailand etc. all stamped and numbered etc. The Japanese copies were always the best