The ways are so easy. You can just go to the store and ask the client whether it is true. According to their experience, they may absolutely give you the right answer. However, you can also check it by yourself by checking the brand, manual work and so on. You can put it on the table to see whether it is in balance. The authentic one must be in symmetry.
Well, the first thing you should do is to make sure where this kind of glasses made is. For example, you can check for a warranty manufacture card and see the label too. So if they print the wrong place, it should be fake one. Besides, you can ask an authenticity guide, and they can give you the professional guide, so that you can distinguish them. In my opinion, the best way is to ask the professional person and that will give you a definite answer.