As a buyer, I am faced with the same challenge as my customers when I acquire jewelry online and at auction: Often no certificate provided, untested stones and hearsay.
Don't be afraid to ask for a certificate from a certified jewelry appraiser before buying. Make sure purity (VVS, VS, SI, I), color (G-H, K-L), carat (stone size or total in "CT"), cut (round, cushion, oval) and suggested retail value are specified in the description.
Use tools such as Info Diamond and Gold Price Calculator to help you determine the approximate value of your find before buying.
Jean A Sarrazin, Professional Picker and President of Veteris Collection Inc.