Well, actually, you should confirm that you get them at a relatively higher price, because Cartier glasses are usually expensive than other brands. Also, you should contact the after sales service to see if your glasses are fake or not. Typically, Cartier glasses are stronger than other glasses, and their surface is well designed, and the craft is sophisticated. So, if you pay more attention to these aspects, you can have higher possibility that you can buy real branded glasses.
In the first place, you should start from observing the brand signal on the frame side of the eyeglasses. If it is real, the signal print will be with no flaw. In the second place, you can put it on the table to observe the balancing character of this type of eyeglasses. Last of all, you can wear it to feel the comfortable character to judge whether it is true or not.