Consumer Reports researched the online cash for gold services. They discovered (not a big surprise) that the online services offered some of the lowest rates. You are much better off going to local jewelery stores or pawn shops.  Here is their advice:

Call several jewelry stores, coin stores, and pawn shops to ask what they pay for gold. If they won’t say, don’t do business with them. Because the price of gold fluctuates, call all the stores on the same day. Most gold buyers, including those our shoppers used, offer more for larger amounts of gold and might negotiate. Try for at least 50 percent of meltdown value.