Amazon provide lots of sunglasses with high quality, but they're very expensive. So, price is the main factor to see whether the sunglasses is real. Then take a look at the comments given by former customers. They can give you lots of useful advice. And the sunglasses is real when they're provide by the manufactures.
By the way, you can buy sunglasses at the official web of glasses firms.
Well, of course, it is hard to say all the sunglasses on Amazon are real ones. But they actually have many types of wonderful glasses products, so you can just have a try. And to spot the fake ones, there are many tips you can apply to. At first, you should surf the internet, and make sure where the sunglasses are made. And then, check the label. For example, if they are made in Italy, you can check the label which should be written with the words "made in Italy". Also, you can check the warranty too. By the way, you can just take them to the official shops, and the professional stuffs can just give some advices.