Sunglasses are often sold as if they are polarized, when in fact they do not have the correct protection. You can prevent this kind of scam by testing your lenses and checking that they are indeed polarised.
There are two easy ways to check if your lenses are really polarized. The first is by looking at a digital screen, such as a phone or dashboard in your car, you will immediately see a rainbow on it.
The second way is to look at the sun. If your vision does not show smudges or blurs when looking at the sun, your sunglasses are polarised.