This report suggests that you exercise MORE than the normal amount of due diligence if you plan on adding any gold or silver coins to your "stack".
There appears (I have not verified this myself) to be a greater-than-normal amount of counterfeit precious metal coin on the market today.
http://www.nbcnews.com/business/business-news/glitters-not-gold-fake-gold-silver-coins-flooding-market-n591201FYI: Note this comment:
"A lot of these fakes are then sold on eBay and Craigslist, or through newspaper ads that promise a great deal on gold or silver coins..."