Where to sell your gold and silver is a fairly complex question with a simple answer--sell it wherever you can get the highest price safely, and after all costs. A couple of important considerations to keep in mind relate to liquidity and transparency.
Liquidity simply means there are lots of buyers and sellers for the item in question. A more liquid item is a 1 oz. gold maple leaf. As I write this, I can buy from my favorite dealer for $1,156 
or sell to them for $1,125. That's a spread (the difference between their buy/sell prices) of less than 3%.
or sell to them for $1,125. That's a spread (the difference between their buy/sell prices) of less than 3%.
That's a great deal! You could also pick one upon ebay for just a bit more. Be careful selling there though, because fees for ebay and paypal will most likely exceed any premium you earn there.
A less liquid item is a handful of old jewelry. Take a handful of necklaces you paid $1,500 for, and barring a huge jump in the price of gold, you'd probably be lucky to sell for $200-300. That's a spread of 400%.
Transparency means that the value of an item is widely known, also works against you as a jewelry seller. As already noted, anyone can easily find current sales prices for common gold coins. Picture a handful of old jewelry. What is that worth? Do you know its purity? Its weight? (In ounces (troy ounces) and in grams?)
The bottom line is that for most of us, the easiest approach to get a reasonable value for unwanted scrap gold or silver is almost certainly going to involve getting quotes from several buyers. That will probably involve schlepping into several "WE BUY GOLD" stores. If the price offered was close, I'd probably settle for 2 or 3 quotes.
To sell coins or bars (where the value is transparent, options include local coin/metals dealers, online dealers, and again, ebay.
Although 99.9% of my experiences with ebay have been positive, I'd be reluctant to sell high value items. Even if a payment clears, there is still a chance, however slight, that a buyer might return a fake coin and ask for a refund. Far fetched? Perhaps, but I'd prefer to sell to a local dealer or a major online dealer.
