Even then it does not hurt to make them aware that you have taken the precautions above. While switching diamonds is outright fraud and theft, false representation can be equally dishonest. The Federal Trade Commission requires that a diamond be within one clarity and color grade of what it is originally sold as. The differences were difficult to discern with the untrained eye and the jeweler had control over both the situation and environment. They determined the lighting, the stones used for comparison, if any, and the words used to describe the diamond.
Most buyers never bother to have the facts verified.
In recent years more and more shoppers ask to see certified diamonds which limits the ability to misrepresent the diamonds grading. Always ask if the diamond is certified. If it isn't, insist that the sale is contingent on the stone being certified. The threat of certification should be enough to keep the jeweler from trying to bump the color and clarity grades. Beware of jewelers not willing to put the facts in writing, but who offer to let you take the stone, prior to the sale, to an appraiser in the neighborhood.