One thing I found out, was to make sure you are getting what you are paying for. I went to sell a gold coin once, and the person wanted to pay much less than the going rate for gold, because they could somehow tell it was once in a piece of jewelry, like a pendant. I questioned this, as we looked at many gold coins and so he brought over his "friend" to affirm what he said. I got much less for that gold coin, for that simple fact that couldn't really be proven anyway.
All I am saying is, that if you can ultimately sell something for much less than you thought it was worth, make sure that you don't pay some other "full" price when you buy it in the first place. You will have lost out on the resale value. As I sold it, I thought. "I wonder if they will sell it as a regular gold coin" as there was no real difference to the naked eye at all. Hope that all makes sense.