Fake sunglasses are not really fakes. They are real sunglasses but they are not what they appear. Fake sunglasses are fakes in the sense that they are copies of expensive designer brand sunglasses and have been created to fool consumers. They will have been made by a rival manufacturer that is hoping to profit from the popularity of someone else's designs. The fake sunglasses copies will be made to resemble the originals as much as possible without looking too obviously false. If a consumer buys quickly without a close look they may well end up with inferior sunglasses. Manufacturers of fake or knock off products do their best to disguise them.
One of the important ways that fake sunglasses will be disguised is with a copy of the original brand logo or name on them. They are often just slightly different than the original marks and a close comparison will show the difference. It will usually have some slight difference so it is not exactly as the original logo. Some companies that make fakes go as far as using an exact copy of the logo although this is illegal. They can make a large profit before this is ever an issue they need to fight. It can be a very large problem for a successful designer to lose sales this way.
You can never really be sure what you are getting when you buy fake sunglasses. You can't even believe that the UV rating they state is true and accurate. It could also be another false statement and your eyes will be exposed to harmful rays when you think they are safe.
