If you are looking to buy or sell diamonds, the best advice is to make sure to purchase or sell a diamond which is certified. Theres are many companies who claim to certify your diamond, but the top rated institution is GIA. The gemological institute of america is highly revered and respected as a staple of the gem and diamond trade. The certificate will cost a couple hundred bucks but it will increase the value of your diamond as well. Your diamond will be easier to sell, hold its value, hold insurance value, and documented as well.