subject: Buying Diamond Jewelry [print this page] Finally for the four C's for buying a diamond, there is the carat weight of the diamond that you are going to have to take into consideration. This is a feature of diamonds that most people are at least relatively aware of. The more carat weight a diamond has the more expensive the piece is going to be, so you can determine how much you are going to have to pay by the carat weight of the diamond.