It's important to understand the difference between the fair market value and the retail price of your ring. The fair market value is how your ring compares with others that have sold in the current marketplace.
Think about selling your home or a piece of art; the process is the same. The fair market value, however, can differ dramatically from the price you, the buyer, originally paid for your ring or what a jewelry store could sell it for to the public today. This latter number is what we call the retail price.
Many jewelry stores will provide sellers with a grading report for their stones. This description may be written by the jewelry store's in-house gemologist or by the GIA. The report will detail your ring's cut, carat, weight, color, and clarity.