Both gold and jewelry made of precious metals have different ratings. They are tested and given these ratings to help determine the quality of the jewelry. The item should have a certificate outlining all of the ratings. The first thing you should do is make sure you are buying jewelry from a reputable source that can provide you with a certificate.
There are different scales of measuring each type of material to determine the quality of the gold or jewelry. It’s important to familiarize yourself with these scales. For example, the word carat is used for both gold and diamonds (for gold it is spelled karat) but represent two different things for both materials. Of course when you go to purchase jewelry, a professional will be able to explain what all the different terms are, but it is helpful to arm yourself with some basic knowledge before going to shop to make the experience much less overwhelming.