If you are buying or selling gold jewelry with a company you have never dealt with before, especially an online business, look the business up at the Better Business Bureau.
Better Business Bureau website

Want to know the current price of gold by weight? This website will tell you the current price:
GoldPrice.org

There are two major certification agencies for jewelry appraisers. Visit the following sites to find an appraiser in your area:
National Association of Jewelry Appraisers
American Society of Appraisers