It is very difficult to tell these days what is authentic and what isnt here are some of my key tips of how to spot anything fake
1)google it first see what price comes up if it is less than 25% of the retail price its probably fake-new stuff second hand stuff will be cheaper obviously.
2)ask where it is from and for detailed pictures legit sellers wont have a problem with doing this if its from somewhere like china or india you can almost guarantee its fake.
3)Dont be fooled into ridculous prices as theses are probably fake and bad quality - i mean why bother buying fakes you might as well go to your local supermarket and shop there people can generally tell fakes (how humiliating) haha.
4)ask the seller as many questions as you can and always reed there feedback and how long they have been around for ,im not saying all the sellers with less feedback will be selling fakes everyone has to start somewhere after all .
5)this ones not about fakes if you import something from abroad you may have to pay import tax and cat which is a lot more than you think so ask the seller if they can arrange for this to be paid or how much it will cost.
Thats all good luck