At equal weight, a diamond, depending on its quality, can see its price quadruple. So don't rush into what you think is a good deal.
First, find out about the quality of the diamond. It is important to distinguish between the total carat weight and the weight of the central diamond.
Most of the time, it is the total carat weight that is stated, but this is not the best indicator as it simply refers to the combined weight of all the diamonds in a piece of jewelry.
Ask your seller about the weight of the central stone, it's Pandora's box, the key part of the jewelry. If you don't know the weight of the central piece, it will be impossible for you to determine if the price is fair. If the seller can't provide you with the information or is very evasive about it, they have something to hide.